You should probably show the entire code that demonstrates the problem, not an ellipsised version - and if it works in other scenarios, show those so their differences can be analysed. Anyway, my guess is your isinstance() checks fail and you don’t set the adjustment. Some diagnostic printing of the results of your checks could help.
I have verified that the isinstance indeed works. I also set the adjustment for most of the spin buttons (yet all of them get stuck on 0). I haven’t checked if it works in other scenarios, although why wouldn’t it? Am I missing to bind some signal which causes this behavior?