I have done a lot of experimentation to get the levelup to work. The following is what I have done and my subsequent findings.
1) If I use the OWC UI, I levelup but am unable to distribute attribute points - in other words I level up as regards level 2, level 3, but none of my attributes levelup.
2) With Darkuid Darn, I get a levelup screen which only allows me to put 1 point on each of 3 attributes.
3) If I then do as suggested by the modder and use his levelup_menu.xml with Darkuid Darn to suppress the vanilla levelup screen, I'm back to the result stated in 1).
I should add all the above is when using the English install.
I then scrubbed that and put in the German install, but using the English esps - gave the same results as before, with an English inventory.
Then tried German install with German esps - levelup works like a charm, but of course everything in the inventory is German, making it troublesome to know what you've got.
So, my theory is that the English esp is at fault, and I wish the modders would comment because it's frustrating to either not be able to levelup or not know what's in your inventory.
Any feedback welcome, because I'd really like to be able to play this mod.
I have also tried copying various things over, but only the German esp enables me to levelup.