Per the passive : Wolf periodically hungers for and hunts jungle monsters.
In a 30 minute match he hunted 4 camps and only during the first 15 minutes. After reaching 6 hunts (two from a champion) he no longer hunted jungle camps. Also, Wolf should howl/bark or make a noticeable noise/remark when hunting a target as hunt targets can go largely unnoticed unless you are constantly looking for the icon on the minimap.
EDIT: Testing this bug with two methods.
First: Grind jungle camps only basing to buy items. Ignore champions and lanes.
Camp - Hunt mark time - Death time
1 -Enemy Raptor 230 313
2 -Enemy Raptor 453 541
3 -Dragon Scuttle 651 723
4 -Enemy Wolf 829 905
5 -Enemy Raptor 1010 1050
6 -Enemy Wolf 1156 1229
7- no mark. Should have spawned at 1330~1340 following this trend. Left game at 25 minutes. No seventh jungle mark
Second Edit: Get 5 stacks from champs then kill marked jungle camp.
Again, Wolf stops marking camps completely. so far 9 minutes without a camp mark.
All tests show that Wolf stops passively marking camps at 6 stacks regardless of how you get the stacks. Marking champions for stacks still works but not jungle camps.