Hi everyone, thanks for the replies
Maybe I'm just overthinking things and should worry less about giving it some welly when swapping films. It does seem strange though. On closer inspection, it looks as though the Ilford ones might be catching on a little piece of metal which is sitting proud of the base of the camera, just in front of the pop-up bit that holds the take-up spool in place. Hopefully I can work it out as I've got another 40 rolls of HP5 to blast through
I also e-mailed Ilford, who reckoned their spools are manufactured to such a precise tolerance they should fit in any 120 camera with ease (as I thought originally). It would be a shock if I ended up with rolls from a dodgy batch haha :S Still waiting to hear back from Fuji....
The camera does take excellent pics, makes me wonder why I've been carting 6x7 gear and a massive tripod all this time when my hand-held test roll provided some of the sharpest photos I've ever taken on medium format... I'm so tempted to save a while and get the 90mm version as well!