I just had a tour of the new Security app and ran by chance into the following problem:

Old app:

1. select the Groups tab
2. 'Add group' action
3. type a name, validate
4. group is added at the root

New app:

1. select the Groups tab
2. 'Add group' action
3. type a name validate
4. dialog closes successfully, but no group is created. Nothing is logged either

I could only create a group in the new app by putting it inside a folder.

This issue is probably worth at least a unit test. Integration test already included in google sheets.