I had an odd visual glitch last night (video uploaded here) where I noticed that some enemies in the area were appearing and disappearing.

I was fighting mudpuppies in the river at Boulder Downs and noticed two "rimy biasts" appear close by - I think they are meant to be levequest enemies? (A FATE started close by at the same time, but it involves fighting energy sprites, not biasts.) Anyway I ignored them and kept going with the mudpuppies, but realised that the biasts were fading in and out of existence the whole time.

I didn't try to engage with them, but was intending to go over and investigate once I'd defeated the last of the mudpuppies - but as soon as I was out of 'combat mode' they vanished entirely and didn't appear again.

Has anyone else seen this happen, or know what was going on?