I have adjusted my RF's, built a sailboat, and work on Mazda rotary engines and Leica finders.

He is my guess, IF it does it in the same place each time, there might be an ever so slight burr on the focus cam on your lens.

My gut says there is something sticky on the roller or the cam or the roller has some damage to the bearing (I havn't had a Bessa here in a while).
BEFORE you go sending it out. Take a swab and clean all your lenses focus cams with some denatured alcohol, or windex on the swab. Do the same with the roller/finger thing in the camera. Likely just some old grease that is sticky causing the issue.
AND if it doesn't bother you, just leave it alone to something else springs up. I found those Bessa Rangefinders to become out of line so quickly I just decided to live with the slight issues... I wasn't using them at f1.4 anyway too often.