FPS drop when moving cursor with vsync

I just noticed that whenever I move the cursor in the game while vsync is enabled, FPS drops from a solid 60 to 30. I'm not sure if this just started happening today or if this had been happening since getting back into the game last weekend without noticing.

It happens whether in the menu or in game (if menu vsync is enabled), in the title screen, etc. Holding right-click in-game to move the camera, and subsequently hiding the cursor, does not result in an fps drop. Manually fixing the fps to 60 doesn't have the fps drop. FPS when the cursor is still is also 60. I am playing the game on Ubuntu with Proton 9-04.

Troubleshooting tried:
-Restarted PC
-Updated and reverted graphics drivers
-Verified game files on Steam
-Different versions of proton (8-05 and Hotfix)
-Removing v4 folder
-Changing graphics settings to low
-Adding "gamemoderun" to the launch options
-I have not modified any game files or installed mods.

It happens even in the main menu, so not related to server settings.