Ever since getting my new 2-piece on my Brewmaster Monk I've been getting severe FPS drops and stuttering with either AdiBags or BetterBags enabled. After a few hours of trial and error I've determined the following:

It only happens when I do a lot of fire damage. In particular maintaining the "Charred Passions" buff on my Brewmaster and pressing Spinning Crane Kick in a large (8+ mob) trash pull with the new 2-piece equipped. This might just be due to a very high amount of combat log events.

It only happens when either AdiBags or BetterBags are enabled. I disabled everything except Bartender4 and BetterBags and I'm practically lagging out of the game. Tried BetterBags after figuring out it was AdiBags causing the problem and it's exactly the same.
I first noticed the issue in M+ but it happens to me when soloing a big pull in Mythic 0 just the same as in a key.

On the same exact trash pull in mythic 0:
Only bartender enabled: no lag, ~108 FPS in combat
Bartender + BetterBags: very choppy, ~30-40 FPS in combat
Bartender + AdiBags: very choppy, ~40-50 FPS in combat

From troubleshooting on Discord, turns out commenting this line in frames\item.lua causes a very noticeable improvement:

events:RegisterEvent('BAG_UPDATE_COOLDOWN', function(_) OnEvent(i) end)

A fix for this has been pushed -- please test the latest version and let me know if this is still happening!

Seems much better now! I'd consider this fixed for BetterBags with 580a075.