After a bit of testing it looks like it can be reproduced using Yanfly Save Core, and I can't seem to get the repro when that is disabled. I thought Autosave was the culprit but I guess it's just the base Save Core.
EDIT: I've been trying to reconstruct the conditions in a fresh project, adding plugins one by one. So far, no luck at all. Sorry this is a bit of a tangled mess for me.
EDIT: I've been trying to reconstruct the conditions in a fresh project, adding plugins one by one. So far, no luck at all. Sorry this is a bit of a tangled mess for me.
You mentioned something about parallel event I have seen many lags caused by these. Even if it runs every 5 frames it can cause severe lag (depending on what it does).