Dehaka not leveling up in co-op prestige 1 level 13

I have Dehaka at level 13 in prestige 1, Devouring One, but he’s not leveling up past level 10 - and he should be able to go to 14 per the rewards. Help?

P1 reduces max level of Dehaka by 4. It is said in prestige description. 14-4=10

Dehaka (the ingame hero) can reach his max level for Prestige 1 (11) at Commander level 14.
While those 2 parallels levels are confusing, I understand your “commander level” is only 13, so it’s normal you still lack a “hero level”.