Yes, issue is definitely caused by One more attempt to fix assert on node activation from Python (6c294f58) · Commits · Graphics / Krita · GitLab commit. I guess they decide to catch and await to execution of every user input from python, and plugin spams it too often. So Krita receieves changes from pigment.o, execute it and only after this try to work with next inputs. Previously, it simply skipped the outdated ones.
Author definitely should to rewrite logic of how Pigment.o interacts with Krita 5.3, it should not spam input events which this commit related, i guess.
This is actually a critical change, may affect for any other plugins for Krita. In one side it is important change, because previous builds could miss old user inputs from user plugins, with this change it execute full input and api calls queues from scripts. But the bad side is performance, if author didn’t make special efforts to manage queues order and didn’t limit rate of api calls.
I can try to make switch in settings, but it seems it will require to restart Krita to apply effect.