Cookie error in user registration

Hello everyone,
We have problems with Keycloak (21.1.1) for some users when registering. The error Cookie not found is always displayed. This happened to 4 of 24 users today. We have already checked the browser settings several times and could not find any irregularities.

Does somebody has any idea?

Best Regards

Robert

I have some Logs before the error exists:

2023-06-01 08:39:33,147 DEBUG [org.keycloak.services.resources.SessionCodeChecks] (executor-thread-11) Will use client ‘plakoda-web’ in back-to-application link
2023-06-01 08:39:33,147 DEBUG [org.keycloak.services.util.CookieHelper] (executor-thread-11) Could not find any cookies with name {0}, trying {1}
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.managers.AuthenticationSessionManager] (executor-thread-11) Not found AUTH_SESSION_ID cookie
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.util.CookieHelper] (executor-thread-11) Could not find any cookies with name {0}, trying {1}
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.managers.AuthenticationSessionManager] (executor-thread-11) Not found AUTH_SESSION_ID cookie
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.util.CookieHelper] (executor-thread-11) Could not find any cookies with name {0}, trying {1}
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.util.CookieHelper] (executor-thread-11) Could not find any cookies with name {0}, trying {1}
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.managers.AuthenticationSessionManager] (executor-thread-11) Not found AUTH_SESSION_ID cookie
2023-06-01 08:39:33,148 DEBUG [org.keycloak.services.resources.SessionCodeChecks] (executor-thread-11) Authentication session not found. Trying to restart from cookie.
2023-06-01 08:39:33,149 DEBUG [org.keycloak.protocol.RestartLoginCookie] (executor-thread-11) KC_RESTART cookie doesn’t exist

2023-06-01 08:39:33,149 WARN [org.keycloak.events] (executor-thread-11) type=REGISTER_ERROR, realmId=xxx, clientId=null, userId=null, ipAddress=xxx.xxx.xxx.xxx, error=cookie_not_found