Check that the back is latched properly. The frame counter mechanism is a friction drive on the film backing, and if the back is not latched tight on both sides it can slip. The back also depresses the frame counter reset tab (upper right with the camera back open).

Make sure the shutter release (on the camera, not the shutter) is not partially depressed. This is normally more of a problem with the C330, but if you are triggering the quick wind-off feature, this will have the effect you describe.

Make sure the frame counter is reset to zero when loading the film. Does it advance with the film wind? If you have trashed a roll of film with this fault, just manually rewind it and keep it for testing - it is better than a roll of backing paper. If the frame counter does not reset, then there is a problem with the frame counter mechanism.

The C33 came in several variants. Some were 120 only, some had the internal frame counter mechanism for 120/220, and some had the external mods for taking the 220 back. The ones taking 220 have a second frame counter reset pin, and a cut-out in the upper right rear of the body to accommodate the large chrome pin on the 220 back.