[johnha]

I had a similar problem with my first rolls (also Fuji). I was loading the film 'start' pointer to the exact position of the arrows in the camera, this often required an extra, complete revolution of the wind-on crank. In practise I found if I left the start pointer a little short of the 120 arrow (at the end of one full wind-on) the problem disappeared. My frame spacing is not consistent, some frames are nearly touching but not overlapping.

In the field you can roughly tell if this happens by where the frame counter is when it stops moving after winding to the end of the backing paper. Mine stops about 'frame' 15 if everything is OK, if it stops earlier than this, it may mean the film had run out by the time the last shot(s) were taken.

[Wheatfield]

The 6x7 is known to have problems with the film advance. Presuming you loaded it correctly, check to ensure the frame spacing is even. If it isn’t, the advance clutch needs to be repaired/ adjusted
I screwed up the advance in my 6x7 by shooting Kodak T-Max film, which had a thicker than standard base. Kodak damaged a lot of cameras with that film. The Mamiya owners association sued Kodak for damages because of the expenses incurred on owners by the film damaging cameras. Eventually Kodak got it and took enough of the thickness off the base of the film to make it usable. I never trusted the stuff after it damaged my camera, I just shot Ilford instead.