I have also tested and confirmed that this bug exists even when all other addons are disabled.

This issue has been coming and going. (or maybe just staying, I'm not sure) I'll see if I can get to the bottom of it.

Issue is still reproducing for me with MogIt v3.10.0.

The issue is at https://github.com/WoW-MogIt/MogIt/blob/master/Core/Tooltip.lua#L92. For some reason the two links being compared are not exactly the same, even though they are for the same item ID / name. Extracting the item IDs and comparing those gets rid of the stutter.

I replaced the line locally with this naive fix, seems to work:

if not (tooltip.item and tooltip.item:match("item:" .. itemID .. ":")) then

this is the answer! thank you so much for this!