sleep bomb issue

Sleep bomb affects all enemy and teammates. I just realised that camouflage monsters and stealthed monsters are still affected by it while they are still immune to stun burst effect. 

Any explanation to this?

Well, if they camouflage/stealth monster is on your team, then it still will affect them. Camouflage and stealth only protect from the enemy attacks. If the monster in question wasn’t on your team, then it is probably intentional. I myself never noticed, but maybe it’s because sleep is a status like poison, so the immunity doesn’t work then.

okay then but It would be awesome if sleep bombs do not affect stealthed teammates and camouflage monsters

Well, then one-on-one would become a whole lot more viable, since you could just stealth a purifier and boom. Three enemies sleeping for almost no cost. Though I guess that’s what Diredemon does, in a way.