27 days ago (from the time of this comments) somebody had the same issue i have.

#438 (comment)

The Party Unit Frames mysteriously disappeared on 2/4 of my screens. Took me awhile but i figured out the only thing in common was the 2 that are still working have pets, and 2 that broke did not.
So apparently if you uncheck enable on the pet unit frame, the party frame disappears at some point (not immediately). To fix this semi-permanently I set the party anchor off from pet and used player as the anchor instead.

Thanks, this solution was helpful

Yes, the anchoring system needs more work since it is possible to break something without noticing.

I had to set the Anchor on the Target frame to None then it show up.