See screenshots. The Dragon slaver cannot be hit by any weapon, tracking ammo will stay on top dancing around a bit, but never hit, other weapons just pass through...
It simply is untouchable for anything, and is deadly to everything.
The Slaver became visible when I disabled SoTP HD.
This looks very like the problem I reported regarding Salvager Nomads (https://ministry.kronosaur.com/record.hexm?id=90343). Does the log show that the relevant image didn't load?
Possibly see also: Ships become invisible and invincible when running low on memory
Had not thought of looking in debug.log, but there it is:
2020-05-28 23:01:03 All resources downloaded.
2020-05-28 23:03:39 Unable to load image: DragonSlaverHD.jpg.
2020-05-28 23:04:35 Unable to load image: DwargMasterHD.jpg.
2020-05-28 23:05:23 End logging session