You have already ruled out a messed-up configuration, and dirt. Good!
I haven't experienced what you describe, but I think it could be static electricity - though I can't really explain why it would only affect one half of the device. Try doing a flat-palm gesture once on both halves before you start gesturing, to rule out static.
You say the diagnostics are all good most of the time. In the cases when the diagnostics show errors, is it always the same sensors that are affected?
Are you moving the device around a lot; could the left half have been bumped hard, or perhaps the middle connector cable slightly pulled?
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