i've been trying to level up depriving skill since ages and I never passed +6. I always use same skill book and no aid materials below +11. Yesterday I finally lost patience and took 22x depriving strike skills from event chests and was pretty sure i will reach +10 easily and still have some books left for later stages. Well, no... I succeeded first try to reach+6, then failed 4 times in a row to reach +2, then I reached +7,+8 once and finally after 22 books I ended where I started on +5. Getting past +6 was almost impossible.
I haven't had event remotely similar experience with any other skill on any other class. So, is depriving skill leveling procedure bugged, broken, does it have different success chances or wth???