I found this information about Tanjis
Tanjis spawns each 3-10 minutes depending on players online, and cannot be blocked from spawning (same as the inquisition bosses, pharaohs and the black knight). Teams can stay in Tanjis' room for 20 minutes, the timer starting when they enter the teleport. Reentry is denied after players gain experience from Tanjis. Thus, teams can earn a few minutes by jumping out and in Tanjis' lair when the first Tanjis is on his last hitpoints. [https://tibia.fandom.com/wiki/Tanjis]
In my opinion all of these bosses work this same method. I remember the day that it was similar with Jaul and we managed to kill him 3 times and for the fourth time on red hp he threw us out of the room.