Overrun by abyssal not appearing in map

I just ran a Molten Vault map that was overrun by the abyssal. The map modifiers said ‘area has 17 additional abysses, area is overrun by the abyssal’. There were also 2 additional abysses from one of my tablets, so 19 total. In reality what actually happened was that only the 2 abysses from the tablet appeared, just those 2, nothing else on the map at all apart from some packs of faridun monsters from the waystone I used.

I believe the map was one of those that was overrun from the effect of ‘stir the swarm’ on the abyss tree, not sure if that makes any difference?