Hey,
From the version gave on the humble monthly Dec 2018 :
I'm lvl 10 with max XP, but I don't level up.
I think it is because I didn't take a new ability before leveling :/
Hello Uranne,
This is a limitation of the Humble Demo.If you become a patreon you can get a newer version that moves past this limitation. (Beta 7 should come out in 2 days)