There are many possible reasons for what you see is happening. Among others:
1) lens out of spec (wobble, loose or wet elements). Inspect the lens.
2) Camera RF cam loose. Check with your finger.
3) Camera and lens RF cams are vertically misaligned (RF cam bent). Open the camera back with the lens on and check.
4) Loose pressure plate. Check with hand/visually.
5) Film didn't sit right on the rails and sprockets.
If 1-4 tests out OK, I am betting on 5). Any irregular frame spacing ? Anyways, if it's 5) don't worry, and spool your film more carefully next time.
Roland.