Hi,
After some struggle, this worked for me:
Go to your server and log in as the user you have troubles with:
Then you will be obliged to fulfill the data required. Only then that error disappeared in my case.
Besides it was interesting to find out that logs and database showed some hints after activating some events in UI at ["Realm settings"/Events/"User events settings"] and ["Realm settings"/Events/"Admin events settings"]
docker run -p 8080:8080 \
-e KEYCLOAK_ADMIN=admin -e KEYCLOAK_ADMIN_PASSWORD=123456 \
-e KC_DB=postgres \
-e KC_DB_URL=jdbc:postgresql://your_postgres_server/keycloak -e KC_DB_USERNAME=keycloak -e KC_DB_PASSWORD=123456 \
quay.io/keycloak/keycloak:latest start-dev --log-level=TRACE,org.hibernate:INFO,org.keycloak.transaction:INFO,org.keycloak.services.scheduled:INFO,org.infinispan:INFO