This is hard to describe but the videos should make it obvious.
I'm having an issue where looking at a certain angle (by actually turning my head - not rotating using controllers) causes my HMD view to go crazy, flipping my head around backwards, and also the pitch axis gets inverted. This is somehow connected to my rotation within the SteamVR tracking space, because using OVR Advanced Settings to rotate the space will also cause the bad region of rotation to move. Using a different avatar and different world makes no difference.
This only affects VRChat. There is no issue in other VR apps, and even overlays open at the same time as VRC (such as the SteamVR menu) are completely fine, it is only VRC that shows this behavior.
It shows both for me in my HMD, and in third-person via a stream camera or for other players in the instance.
This is happening on VRC Open Beta build 1342, with a Pimax 5K Super, using the new Pimax Client (not PiTool). I was able to replicate this across system reboots. It only happens on the new Open Beta, and the non-beta version of VRC is fine. The issue does not occur using a Quest2 + ALVR. A friend also on beta using a Quest2 + Virtual Desktop did not have this issue.
Videos:
View in first-person: https://youtu.be/x9cpQ9aFQCc
View in third-person (had my arm outstretched to show how I was rotating IRL): https://youtu.be/njKve55cEVo
Showing that an overlay is fine, only VRC is wrong: https://youtu.be/ENOoEnD9b94