That's what I'd try, just suppress the diagnostic and let it rip.

I did and it got accepted.   let's hope client don't get any weird IRS notice.

DID YOU EVER GET A NOTICE FORM THE IRS ON NEGATIVE AGI ON FORM 8962? DID THIS CAUSE ERROR IN NEXT YEARS PRC? THANKS FOR YOUR INPUT NOT FOUND ANYONE WHO HAS A CLEAR ANSWER..

I also don't have an answer for you, but I would not expect this to generate a notice. I know that doesn't help finalize it, but I wouldn't worry about a notice and just deal with it if one comes.

I would get an 8821 in place on the client(s) so you get a copy of the notice as well if one comes so that you don't have to rely on the client to provide it to you. I'm starting to make that my default on clients now.

I filed one last October (can't remember if I had to disable the diagnostic). So far, no push back from the IRS.  Go for it.