I see the joins are timing out, that is probably due to security group config if the cache config works. Just check if the JGROUPS_PING table in the keycloak database is populated. If it is not there is something wrong with the config. Else it probably is the security group prohibiting communication between tasks.

Make sure the ECS service has a high enough load balancer timeout as well, since it can take some time for Keycloak to respond in health checks.