Bombs will sometimes go invisible when dropped. Mostly happens during intermission and just before the wall raises in the new area. Phase 3 planet cracker is also invisible except for maybe furthest one from the boss. The visual bug doesn’t affect everyone the same.
EDIT Video of bug
When the rogue(with 3 chat bubble above head) drop the bomb you would see it for a fraction of a second at 0:03 back right leg. Once dropped it stays invisible to the healer’s pov, there was no indication of a bomb there until our outlaw rogue picked it up again. Some people in the raid could see it and others cannot.