Hmm, it looks like an issue with your webcam not picking up your face at certain angles maybe. Does the same thing happen if you use the app at that angle without games running?
One messy solution might be to go into the face tracking settings and try turning off the "fall asleep when tracking lost" option and see if that helps. If it does, you may want to try manually setting the FPS in vtuber kit on the Gear tab to something like 60fps. And then try re-enabling the fall asleep option. That may make a difference.
Let me know what you find out, it'll help me with making my next update for the app!