Elemental Invasion bosses despawn instantly after killing them

[GrenderG]

Current behavior:
Elemental Invasion bosses despawn instantly after killing them.

Expected behavior:
They should have the correct respawn or at least don't despawn 5 seconds after killing them.

Steps to reproduce:
Tested with Tempestria and Avalanchion and happened with both of them, you kill them and they despawn in 5 seconds, more or less. Doesn't matter if you kill the adds first or not. Don't just spawn the NPC and kill him because the respawn time will be 10 minutes, for this bug to happen you must kill them when the actual event is happening.