Steps to reproduce:
1) Create application.
2) Create "event class family".
2) Add "event family map" to app
3) Create endpoint user.
4) Attach clients to new endpoint user
5) Send events between clients
6) Detach one of the clients from existing endpoint user.
Actual result: Got error on operations server about null user id. Tenant actor with child actors was restarted.
Expected result: No errors.