I recently returned to using the polaris lance and noticed what I can only assume to be a bug. When using the lance's explosive bullet, if you fire too fast (while the explosive is warming up) the explosive round just vanishes, and does not appear to do any damage or inflict its burn. I have only tested this in Gambit Prime and in the tribute hall, but I would assume it is the case everywhere.
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Looked at this myself, works in general PvE too, tested outside Osiris on mercury. You don't even need to shoot the enemy again, just shooting anywhere, even on the ground, destroys the explosive round.