If Selfie Expression Quality Level is for whatever reason set to "off" when Vrchat starts, enabling selfie expression results in an (logfiles say at least) unreferenced object error, spamming the logfiles and giving repeated ingame notifications about the webcam being potentially in use. Only way to stop said spam is to close and restart vrchat.

Setting a Quality level which is not "off" before enabling selfie expression solves the issue.

Here is a video about said behavior.