[Gameplay] Sion's Passive Bugging Out

So Sion's passive normally gives 10 HP for every large monster killed, and 2 HP for small ones. Okay. That's great. However, over the last few games, I've found that his passive sometimes either gives him 2 HP for a large monster kill, or none at all. The happens for the entire game, and about 5/8 times I've played, I've dealt with this. Maybe it's because I play him in the jungle, but Sion can't Sion without his passive working. As the bug just seems to happen randomly in games, without any steps needed, I don't have a guide to reproduce it, though I don't think it's needed in this case. Can some assistance be provided in saving my main?