Firstly, this isn't the right subforum; there is a Bug Reports subforum.

Secondly, what "update announcement" are you talking about? The only sort of official reduction of EXP was with the launch of 6.0, which only lost the half-filled EXP bar for your current level and did not level anyone down. (Also, if there was an official announcement then it wouldn't be a glitch.)

Thirdly, if they were lowered to 80 then you could not access Zot with them anyway.

Fourthly(?), you definitely have your endgame dungeons mixed up, because trusts can't run "the one with prototype Omegas and cyborg dragons", although they can run the Dead Ends which has neither of those things.

Altogether I would guess that you haven't been using trusts at all, but the duty support system. (Similar function, different menu.) It lets you pick any trust-compatible dungeon without having levelled the trusts, but they do not receive EXP. That's the only way you could be running a level 81 dungeon with your trusts at 80.