Sorry for the delay - I had to reinstall the VM a couple of times, managing to brick it during 3D initialization (Win11 and HDDs...).
Turns out it is "locale" related - namely regional formatting - if my format is being applied then I cannot use assets and models as they simply will fail to load (and I will have the exact same behaviour as before - some buttons not working at all).
If I switch to US formatting - mod fully works, models load and no issues are being observed. Except one - my values from previous save are completely out of whack - if I supplied (via slider) value like 6,8786845 (comma being the decimal point) - now it reads without the comma and goes "through the roof".
I am still looking to see what exact regional formatting option causes mod to stop operating normally (I tried reading the log file game creates but no luck so far) - so I have to do some trial and error until I find the specific option that causes the mod to break. Will post an update hopefully soon.
EDIT: ugh, it's a bit difficult to test - basically any "available" mangling with English US (or other English) regional formatting doesn't really cause the modded game to fail loading assets/models data.
But changing to any "comma as decimal point" regional formatting (so far I tried Albanian and Hungarian) - will "break" the mod from loading.