After the recent hotfix to fix the problem with druid shapeshifting mentioned in this thread:
the TBC Classic game client has started to microstutter whenever player models load in on your screen. The stutter happens at the exact same moment that the UPDATE_SHAPESHIFT_FORM event gets sent to your client, tracked in the event log in-game. This is happening with no addons installed.
I recorded a short video showing the problem here: