Whenever there is a space or "&" or German characters in the group name, it is giving us the blank list instead of the usernames. This is happening with the 2.5 version of the app.
We can confirm that a space in the group name causes this problem. Please note that we use other special characters too, e.g. ‘&' or German umlaute (’ö' etc.).
Just checked and we get the same problem when using '&', e.g. ‘FDS-DataProduction-GDN-Obstacles&Airspaces’.
~ I have included this fix in the develop branch. You can validate it and also demo all the DELGROUPS issue to Marketing using this artifact