Thanks for trying. This makes it even weirder for me
The only thing I installed in Fusion on the Linux machine is the latest Reactor (to have easy access to a few scripts, cryptomatte and lens flares). The Windows machine has a fresh install of Fusion. Both show the slider problem.
I have no idea, except that my locale is set to German on both systems (which caused problems a few times during the last 20 years, like Softimage not executing certain scripts or Krita's OCIO failing due to "." and "," being used differently.)
Noone else here having this problem?