[BUG] Ghost or ghost-like monsters in netplay (invincible monsters that can interact with and hit players)

[Acts19quiz]

Describe the bug Sometimes in online netplay (Cooperative, Horde, and maybe even Deathmatch if monsters are enabled there), monsters can enter a state where they're invincible, but can still interact with players (collide with them, damage them, etc.), and exhibit other odd behaviour like disappearing. The symptoms are similar to the classic Ghost monster bug, but Arch Viles aren't needed for this.

Build that the bug occurred in 10.3.0 GB28EE-8578

To Reproduce I don't know any precise steps to accurate reproduce this other than to play a bunch of Cooperative or Horde, then wait and see.

Expected behavior For monsters that are killed to stay killed, or otherwise if a net desync happens to be at fault, that 'ghost monsters' are prohibited in some way from interacting with clients.

Screenshots, NetDemos, & Crash Dumps Here is a netdemo demonstrating the issue. It uses DOOM2.WAD and HORDAMEX.WAD with Odamex 10.3.0. Here's a timeline of this bug:

5:00 Lost Soul 5:35 Lost Soul 5:50 Lost Soul disappears 5:55 Lost Soul 6:35 Lost Soul 7:52 Lost Soul

At 5:50, one of the bugged Lost Souls actually disappears. That makes it seem like the +39 cell ammo thing where it's missed packets or something, but here we're dealing with more than just information syncing up: It's monsters actually still effecting the client. It's also worth noting that it's only Lost Souls that this happens with. What that means, I don't know.

Additional context none

[cuantar]

I encountered this in Eviternity. Another feature of the Ghost Monsters is that they can sometimes walk through closed (or closING?) doors.