Reason;
#1. the eth address connected although is unfounded (this happened to my friends).
#2 they didn't accept appeals,
#3 they don't want pay because your stake in the bounty tables is too much you got a lot reward than others, the choice is decreasing your reward or they will find your mistake to made an reason to do not pay you (sounds weird but it's a fact on some bounties)
p.s: i don't want mention which bounty