In the previous version, I could do the following:
I tried to do this in the new version of AIO 1.13, and it broke the Edit Field Group Page.
The fields completely disappear and I can no longer edit them. So I had to revert AIO versions, and it works again.
I can't be sure which caused the problem but I think it's either A) nested groups B) fields with identical ID within nested groups
I appreciate you looking into this issue.