Raid suddenly stops

There was a raid ungoing. It was have 3 or 4. The bar was filled half, but there weren´t any illiger, witches, vindicators or other raid mobs (I checked in spectator). suddenly the bar disappered and I found an evoker with some other illigers (quite far from the center, but the evoker wont spawn outside of a raid). After killing them nothing happend.

I had problems befor of missing illiger mobs. Never managed to complete one raid.