rx8 - strange behavior

Might be a bit of a long shot but I have seen people that have had similar problems and it turned out that there was components that have broken loose off the board. Apparently it's a reason why Tekin has made the new cases to combat the issue of components coming loose off the board during impacts.

That isn't my pic but it might show what i am talking about. The guy with that ESC had same problems as you are describing.