it is indeed very random - for ag_uf.
i have never had a prob with Grid creating a frame.
but i;ve never done a /reload ui while in combat also. the only thing related that i've seen, if i get DC while in combat and log back in combat (boss fight) grid fails to appear at all (no frame created)
what i've seen these past few weeks, is in BGs - with ppl coming and going all the time, grid allways displayed all BG members correctly, while ag_uf would sometime show me and one other person while the party was full.
if it;s a secure frame creation problem, maybe ag_uf could delay the creation until after combat. or try to create it in combat, see if it fails, and than try again after combat (if such a thing is possible at all)
when someone joins the party while i;m in combat, the frame is not visible (but it highlights and i can see the buffs and target). it happened sometimes before 3.1, but now it;s constant.
it never happened in pvp/BGs, but now i see it all the time
(grid does not have this problem, so it;s not a blizz issue)