Reply To: My friends and group have all disappeared!

The obvious solution might be to get invited by them to be a a friend of them and be invited by them joining the group again.

Friendships and group joining needs to be confirmed from the other side (probably in a certain time interval).
The only exception is an open group for everybody.

Maybe the friendships were not confirmed.
I have no idea what happened to the group you have been a member in.
Maybe a bug in the software.