As per the title, in Beta 2.8 and continuing in 2.9, the motion controllers of the Reverb G2 act in a repeater mode for buttons A, B, X, Y. Example, Y is set to Escape Menu, and even just tapping Y will open and close the Escape Menu five times in a mere second.
I had previously ran the game under Steam's VR for the majority of 2.8 beta, in which case the buttons functioned normally... i.e. click or click and hold only registered as a single button click.
Now I imagine it's something with how OpenXR interprets the input devices (motion controllers) but I can't seem to find any option to configure otherwise.