Blaze and skeleton drop issue.

I build a skeleton xp farm and when I spend 25 minutes of grind xp and drops only 8 bones droped with 100 skeletons droped but arrows and bows is dropes normaly. In nether I killed 20 blazes and get only 1 blaze rod. I don't know other mobs drop items normaly but I only found this issue with skeletons and blazes. My device is Samsung galaxy J7 2017