User federation: LDAP Sync from AD successful, but no users synced

Hi everyone,
Im trying to use our Microsoft AD for user federation via LDAP.
I set up everything best to my knowledge, connection and authentication tests are successful.
When I click on ‘Synchronize all users’ I get the message

**Success!** Sync of users finished successfully. 0 imported users, 0 updated users

which of course shouldn’t be the case as there are about 1600 users.

The log says the same:

2021-09-12 12:04:05,135 INFO  [org.keycloak.storage.ldap.LDAPStorageProviderFactory] (default task-4) Sync all users from LDAP to local store: realm: MYREALM, federation provider: ldap
2021-09-12 12:04:05,284 INFO  [org.keycloak.storage.ldap.LDAPStorageProviderFactory] (default task-4) Sync all users finished: 0 imported users, 0 updated users

So I changed the Log level to debug and found the following error in the server.log:

2021-09-12 12:54:08,487 DEBUG [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-8) could not log warnings: java.sql.SQLException: IJ031070: Transaction cannot proceed: STATUS_COMMITTED
        at org.jboss.jca.adapters.jdbc.WrapperDataSource.checkTransactionActive(WrapperDataSource.java:272)
        at org.jboss.jca.adapters.jdbc.WrappedConnection.checkTransactionActive(WrappedConnection.java:2007)
        at org.jboss.jca.adapters.jdbc.WrappedConnection.checkStatus(WrappedConnection.java:2022)
        at org.jboss.jca.adapters.jdbc.WrappedConnection.checkTransaction(WrappedConnection.java:1996)
        at org.jboss.jca.adapters.jdbc.WrappedConnection.getWarnings(WrappedConnection.java:1125)
        at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.handleAndClearWarnings(SqlExceptionHelper.java:290)
        at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.logAndClearWarnings(SqlExceptionHelper.java:269)
        at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.releaseConnection(LogicalConnectionManagedImpl.java:194)
        at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.afterTransaction(LogicalConnectionManagedImpl.java:162)
        at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.afterTransaction(JdbcCoordinatorImpl.java:274)
        at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.afterTransactionCompletion(JdbcCoordinatorImpl.java:452)
        at org.hibernate.resource.transaction.backend.jta.internal.JtaTransactionCoordinatorImpl.afterCompletion(JtaTransactionCoordinatorImpl.java:381)
        at org.hibernate.resource.transaction.backend.jta.internal.synchronization.SynchronizationCallbackCoordinatorNonTrackingImpl.doAfterCompletion(SynchronizationCallbackCoordinatorNonTrackingImpl.java:60)
        at org.hibernate.resource.transaction.backend.jta.internal.synchronization.SynchronizationCallbackCoordinatorTrackingImpl.afterCompletion(SynchronizationCallbackCoordinatorTrackingImpl.java:72)
        at org.hibernate.resource.transaction.backend.jta.internal.synchronization.RegisteredSynchronization.afterCompletion(RegisteredSynchronization.java:44)
        at org.wildfly.transaction.client.AbstractTransaction.performConsumer(AbstractTransaction.java:223)
        at org.wildfly.transaction.client.AbstractTransaction$AssociatingSynchronization.afterCompletion(AbstractTransaction.java:306)
        at com.arjuna.ats.internal.jta.resources.arjunacore.SynchronizationImple.afterCompletion(SynchronizationImple.java:96)
        at com.arjuna.ats.arjuna.coordinator.TwoPhaseCoordinator.afterCompletion(TwoPhaseCoordinator.java:545)
        at com.arjuna.ats.arjuna.coordinator.TwoPhaseCoordinator.end(TwoPhaseCoordinator.java:101)
        at com.arjuna.ats.arjuna.AtomicAction.commit(AtomicAction.java:162)
        at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.commitAndDisassociate(TransactionImple.java:1295)
        at com.arjuna.ats.internal.jta.transaction.arjunacore.BaseTransaction.commit(BaseTransaction.java:126)
        at com.arjuna.ats.jbossatx.BaseTransactionManagerDelegate.commit(BaseTransactionManagerDelegate.java:94)
        at org.wildfly.transaction.client.LocalTransaction.commitAndDissociate(LocalTransaction.java:78)
        at org.wildfly.transaction.client.ContextTransactionManager.commit(ContextTransactionManager.java:71)
        at org.keycloak.transaction.JtaTransactionWrapper.commit(JtaTransactionWrapper.java:90)
        at org.keycloak.services.DefaultKeycloakTransactionManager.commit(DefaultKeycloakTransactionManager.java:136)
        at org.keycloak.services.filters.AbstractRequestFilter.close(AbstractRequestFilter.java:64)
        at org.keycloak.services.filters.AbstractRequestFilter.filter(AbstractRequestFilter.java:49)
        at org.keycloak.provider.wildfly.WildFlyRequestFilter.doFilter(WildFlyRequestFilter.java:39)
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
        at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
        at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
        at io.undertow.servlet.handlers.ServletChain$1.handleRequest(ServletChain.java:68)
        at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
        at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
        at io.undertow.servlet.handlers.RedirectDirHandler.handleRequest(RedirectDirHandler.java:68)
        at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:117)
        at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
        at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
        at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
        at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
        at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
        at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
        at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
        at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
        at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
        at io.undertow.servlet.handlers.SendErrorPageHandler.handleRequest(SendErrorPageHandler.java:52)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
        at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:269)
        at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:78)
        at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:133)
        at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:130)
        at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
		at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
        at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1530)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1530)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1530)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1530)
        at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:249)
        at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:78)
        at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:99)
        at io.undertow.server.Connectors.executeRootHandler(Connectors.java:387)
        at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:841)
        at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
        at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1990)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1348)
        at org.xnio.XnioWorker$WorkerThreadFactory$1$1.run(XnioWorker.java:1280)
        at java.lang.Thread.run(Thread.java:748)

Does this give a hint to anyone, what might be the problem here?