"Hmm, maybe it's just the saw. Great tip for the threaded knob, blade changes can be a giant pain. What knob did you get? Just any old little knob that would fit from your local hardware store?"
I took the Allen set screw out of the upper blade holder and found a knob with the same threads. Had to cut it shorter and grind the end flat. Then polished the end with wet/dry sandpaper so it won't dig into the blade. You could probably take the set screw to a hardware store and find a knob that would work. These were in my shop drawer. I'm.not sure where they were from.