I have had the same issue with my EX-21. The first time it happened I removed the top plastic piece and checked for lose parts. Didn’t find anything so put the plastic top on again. Saw ran normally for quite a while. When it happened again, I blew compressed air into the space by the top arm. Saw settled down again. I found if I ran it at full speed it generally pulsated, so I always ran it at a little under full.
The saw was practically brand new when I bought it, after a while it seemed to break in, and I could run it full speed if I wished and it would act fine. Not sure how new your Jet is, but it could just need broken in.