SLO not working with external IdP

I’m new to this, so some of important info might be missing.
I have set Keycloak (v11) as an identity broker and set Auth0 as SAML identity provider.
For the integration of Keycloak on the web sclient I’ve used the Java Servlet Filter Adapter (Securing Applications and Services Guide)
The login works okay, but it looks like, on logging out, the user is logged out from Keycloak, but not from the external IdP. I’ve checked the Auth events and there is no log out event, so it looks like Keycloak doesn’t actually call the logout endpoint of Auth0.
When logging out, I’m using RefreshableKeycloakSecurityContext.logout(KeycloakDeployment deployment).
I am not using backchannel logout.

Is there something I’m missing?