add attachments button missing in "New Item" form of an SPO list

Haven't had any responses yet other than the folks here confirming the issue.  I've done a lot more testing and asking around.  There are a minority of people in our tenant that this isn't happening to yet... I told them to keep me in the loop because I suspect it's just a matter of time and gave them the info to go back to the list's "New" button.

I am still looking into the issue and will update if I ever really figure out what the problem is.. but I'm not hopeful that I'll find anything.  Likely as mysteriously as it started it'll mysteriously start working again.