Yes, it could be the polyswitch. I had the impression that he was scanning pretty wide and fast -- really a bit too wide and bit too fast for these scanners to keep up.
If you stop the laser input (i.e. go to basically a black frame, or press STOP) and wait just a few seconds, and then press PLAY again, does it immediately come back to life and work well again for a while, or is the situation that when X axis is freaking out, it will stay freaking out? Basically, after it freaks out, what do you have to do in order to get it to work normally again?
If it will stop freaking out after just a few seconds of rest, then it's just the the polyswitch is opening up to protect the scanner, and this will be an indication that you're simply pushing them too hard.
Bill