This was happening to me with my EX21. I found that I was pushing the lever to far back and it was hitting the arm while it was going up. The fix was to only push it up just past the 12:00 position, it still locks the lever but clears the arm while in operation.
This conversation is had at my booth numerous times. Even when you tell some of the people it is done by a Scroll Saw the roll their eyes and say sure it is.
There was another topic on this last week. I have never had this problem with my Ex but do with my Jet. The topic had a few different tips on how to fix it, one of which was using a rubber band to hold it in place. I used that on my Jet and it worked great. Take a look at it.
Finished this series of the Butterfly crosses. Walnut, Poplar, Red Oak and two Red Cedar. Plus, had a little extra time to day and did two fun ones that I found in SSV Vault.