Confirmed and root-caused; fix in progress (not shipped yet). Server-authoritative monsters are on, but the server only simulates monsters that come from a map's fixed spawn data. Area mini-bosses (Faust, Stumpy, Zeno, Dyle) are spawned by a separate system, so the server doesn't know about them and each client removes them about a second after they appear — that's the "instant die." The fix is to have the server own these bosses too; it's a larger realtime change I'm actively working. No re-test yet.

Root cause fixed and the SERVER side is deployed + verified live. The server now adopts client-spawned bosses it didn't previously know about (area mini-bosses, and also Zakum/Papulatus/Horntail which were outright unkillable for the same reason), so they're no longer removed on sight and take damage normally. I tested it end-to-end against the live realtime server: a reported Stumpy was adopted, stayed in the world, and died to damage. The matching CLIENT change (which tells the server about these spawns) is on develop and reaches players at the next publish — so this fully lands for you once the game is published. No re-test until then.

Live in the latest publish — marking this Fixed. Thanks for the report!

It looks like the Timer boss in Ludibrium is still dying to the bug. I have tested Zeno and Faust and they're both fine.

Thanks Kiji — you're right, and it's a good catch that Zeno and Faust were fine while the Timer wasn't. Root cause: the earlier fix makes the server "adopt" the area bosses the game spawns, but the Path of Time / clocktower maps in Ludibrium are ones you climb through in just a few seconds. On those, the Timer's spawn message reached the server a split-second before the server finished registering that you'd walked into the new map — so it filed the Timer under the PREVIOUS map, the boss was missing from the map you were actually standing on, and the client removed it about a second later (the fade-out you saw). Single-arrival maps like Faust's don't hit that timing, which is why they worked.

Fixed: the server now files a spawned boss under the map the client reports it's on, which sidesteps the race entirely. It's a server-side change and it's already live — nothing to update on your end. Please pop back to a Path of Time map (Lost Time 1/2, or Whirlpool of Time) and let me know if the Timer sticks around now. Thanks again for the precise repro — it's exactly what pinned this down.