This problem has to do with Moodle boost theme (and also present in Boost Union).

It's about the selection for groups on the submission page:

As you can see, the group selection drop down menu is not useful at all. First, there's the group picture (which I bet almost nobody uses) and then there's to little space left for the group name.

We auto-generate groups and the first part of the group starts with a group code. Trying to find the correct groups is cumbersome.