This is an hard to fix issue honestly.
I have already "fixed" the issue by limiting the amount of chests per chunk to 512, same for hoppers. However stashes built before this logic was implemented are massive and lag the server. Luckily only a few of them exist, but they do significantly drop the TPS for a short amount. I have already tried looking for solutions but due to the nature of Minecraft there is almost nothing possible one can do that would fully fix the lag clean and nicely as it is a very technical issue.
PS: Yes we tried everything possible(Switching to Folia, limiting render distance, slowing chunk loading for chests, lazy reloading big NBT chunks etc etc)
And we do not want to just world edit people bases out as it would compromise on the no admin intervention aspect of the server which morally feels "wrong".
TLDR: Not much we can do about it, and the issue is already fixed for the "future". But we appreciate the feedback.