To be certain, keep the film out of bright light after removing it from the camera. Most times I can leave an unprotected exposed roll of 120 on my desk, say, without any problems. But every now and then a roll shows what you describe.

I've never used an RZ67 but maybe the removal of the exposed spool is easier on its back? The Rolleiflex can be fiddly and can allow for a bit of unwinding of the film while oyu try to grab an edge and hold the spool knob out and such at the same time.