I experienced the same yesterday for the first time ever and only in Classic.
I copy/pasted my macros one by one to a txt file and deleted them in-game. Did a /reload ui and played for two hours. The FPS drops where gone. I then pasted the macros back and did another /reload ui and I’ve been playing ever since -sleep. So far so good. No sign of FPS drops.
Never disabled another addon except NeatPlates which seemed to trigger the drops faster in crowded places. Running with NeatPlates and a sh*t ton of addons active again.
No more FPS drops for me.