Here is a useful tool for figuring out why your Form Sets aren't working the way they should.

However, also be aware that in an update in the late summer of 2022 Microsoft introduced a bug in a Word update that interferes with the operation of the Sets feature.

If your Sets once worked but now do not, perhaps allowing only 1-2 forms at a time or none at all, the Microsoft bug is a good suspect.

Here are two articles that address disparate causes, one of which will solve your problem

When a Set fails, a Microsoft Word Bug May Be the Cause https://kb.theformtool.com/202698186-What-to-do-when-things-turn-hot/360049245693-When-a-Set-fails-a-Microsoft-Word-Bug-May-Be-the-Cause?from_search=108090938

and A Bug From Microsoft, Build 20088 at https://theformtool.helpjuice.com/admin/questions/1556869