[K David]

what do you say? the tank?

I'm going to stick with the way that the camera spooled the film onto the spool, but I'm open to the possibility that it's the tank. However, if you did everything the same and the subsequent images developed in that tank are fine, then I think the tank becomes a less likely culprit.

[Digitalis]

what do you say? the tank?

I think the developing chemistry is fine* there is definitely something going pear shaped with your developing tank. The fogging pattern on the film isn't consistent though, I have no experience with loading film on the Mamiya 645TL - but if it is anything like the Bronica SQ, for the love of god keep the film taught enough so it will be smashed flat against the film rails, maintaining friction here is important: if you don't it will bog down halfway through the roll and you will get edge fogging when you unload the back. Also film backs like those used in the Mamiya 645 TL can develop light leaks near their hinges - just something to be aware of.

*the shadows are blocked up though, don't be afraid to overexpose negative film as you have TONS of latitude compared to transparency films. Shadows are always the grainiest part on negative films, overexposure minimizes this.