I run 4 monitors my self, I have not seen anything like that. so I don't think it have do to with multi monitor setup. There is nothing really with that, that should affect it. unless you have some multi monitor third party programs that does something.
However if you have different dpi settings for each monitor, it can take Window a short time to scale it correctly
And also if you have a lot tabs it might be that it refreshes (rescan) the tabs, and it can also depend on how you drag.. from or to external programs.
Also lots of external program that hook them self into MC can affect it
You can active logging in core settings. But I don't think it will give much.