It does sound like an issue with the driver, and it's a shame for your challenge map, but I'd be more concerned with getting this sorted, as it could be weeks/months before there's a new driver.

I know you said Krita crashes a lot for you, but what would happen if you opened a small file, say 250x250px, and just drew a few squiggly lines with your tablet. Do you get any issues/oddness with Krita? Just wondering if it's a Gimp-only problem, or a system wide tablet issue that affects every drawing program.