Found this thread on googling. I had the same issue with my Stages crank - identical to OPs pictures. The central plastic screw had the outer edges chewn off and the crank arm slipped to the position of the drive side.

I found my Allen key screws to be loose afterward. These were torqued to the correct spec.

I've had the power meter for years but have not cycled much at all over the last 2 years and infact this was my first ride this year.