ISSUE SUMMARY:
Currently there are 5 valid members in the database.
How to see in the screenshot from below in the members tab the sum of members is 2.
Same to see on the group panel but the number of members in the group must be 5, too.

RESULT

Meanwhile I deleted the group, because the chaos with it is greater.
So I could show the members but ever one member kept missing.
I'm in hope it will be better wehn I create a new one.
Thus with this action I have the next issue...

Strange!
OK, now it works.
But do I have to calculate with such an unstable behaviour with groups?
Than you should give us a tool to re-organize existing users in a new created group.
The other error was the issue with the missing description field.
I found the solution here in the forum with activation of the TinyMCE editor.
That's not so optimal, because each activated editor more can decrease the performance.
Why not an editor of my choice?