I doubt this is the case here but I have seen fogging from removing the tape holding the film to the spool. It caused static and was visible in the darkroom.
Since first using 120 film back in the 60's I've never had a problem with film spools from any manufacturer, and I've used Agfa, Adox (original), EFKE, Foma, Fuji, Ilford and Kodak, oh and GAF. After all millions of rolls of 120 are used each year, and its a mature film format.
I can understand your frustration, something has changed. Get another APUG member local to you involved a second pair of eyes may see something simple that your over-looking.
Try a test using a new sealed roll of Tmax 400, leave it unexposed and only undo the sealed wrapper in the darkroom, obviously in the dark and load and process as normal. If that shows even a slight trace of fogging then you'll know its a darkroom/processing problem.
Ian