[keycloak-user] ldap group-ldap-mapper needs up to 60 seconds to add a user to a group

We are using keycloak 3.4.3-final with an ldap user federation. Users and groups are created in keycloak, and from there automatically written to an openldap servers, since some application can only access them over ldap. So the "edit mode" is writable and "sync registrations" is activated.. The group-mapper is configured as ldap_only. Creating a new user is lightning fast. But if I add the user to a group, where already around 1000 users are members of, it takes around 60 seconds to add it or also to remove it.it was faster when the group had less member, but we can watch how the time grows the more members that groups has. But it was already slow when there were only around 100 users, then it took around 10 seconds to add the user to the group. When we add the users to th e groups directly in ldap it works in miliseconds. So the problem seems to be a keycloak one. In total there are maybe 2000 users and 15 different groups. Keycloak is running in a docker container. Anybody experiences similar problems? Or has any ideas what we could change? We already tried to change the "User Groups Retrieve Strategy", disabled the ldap cache. disable connection pooling and pagination. But nothing seems to work. thanks in advance michael