From long time my Max Bounty Collected not increasing at all even increasing Bounty wins and kills. I don't understand why ....
This stat tracks the largest bounty that you have ever claimed. So even though you have since gotten more Kills, if the payout was not larger than "Max Bounty Collected" this is not going to change. Also, where are you looking at this stat? If you view it from your own Profile it should be up to date. If you are looking at the leaderboard that could be up to 24 hours of out sync.