I just checked on Halescourge at the broken bridge: All monsters have animations for jumping over gaps and they use them.
I also checked that location on Festering Ground. With only me and the monster being on the map, all monsters pathed as expected and they jumped over the gap using their animations. Some things felt off, however, as this gap requires a rather wide jump so the animations don’t match the distance all the time. They’re also kinda ‘sped up’ because of the distance. The Chaos Spawn, for instance, kinda landed midair and teleported the rest of the distance straight to the platform where its attack animation started to play.
So, I assume that under certain circumstances animations can get lost. Latency might also be a factor (like enemies walking through air) even though the clips in OP are from the host POV.
EDIT: I managed to reproduce the Troll teleporting:
Now, TBF, I teleported quickly to the other side myself. But this might happen naturally ingame when the Troll switches aggro from one player to the other. So, in OP’s clip I think Saltz took aggro by shooting the Troll and everything else seems identical to my clip.