elgg 1.6.4 upgrade to 1.7.7 --> Groups are not showing up

hello elgg support

I wanted to upgrade my site to the 1.7 release (I'm currently at 1.6.4).

After upgrading (files&db) everything works fine except the group mod.I cant see my created groups anymore in the version 1.7.7.

I restored the backup and I updated my site with every single version.

1.7.1 still works fine.

the broken group problem starts with version 1.7.4.

I still can see the numbers of created groups - but the  groups itself are not visible.

(p.s. I also removed all mods which got not distributed by the core version)

Any help would be greatly appriciated.