After spending 1 hr finally found the loop hole. IM is influenced by Battery and data sense. there is absolutely no need to resent your phone or remove and readd FB account. follow below process to make it work.
1- open data sense - > Set to no limit( non Specified ) and
off the Restrict data and restrict background .
2 - Open Batter saver and turn it off
3- Go to setting and flip around. you will see list of options like internet explorer, background tasks , etc.....
4- after following instruction 3-- open background task. you will see list of applications working in background you will option of
battery. blocked the option.
5- go to IM and see the magic.