If The Immersive Engineering floodlight is active within 27 blocks of the portal it causes all hostile mob portals to stop working completely. It seems to be an intended part of the floodlight, but other mob spawning prevention tools (like mega torches) do not stop portals but the floodlight stops it completely and just makes the portal expire.

(was not able to get a video in a way to add to the report but the image attacked shows what the portal looks like when it tries to spawn the wave while the floodlight is active.)

The portal acts like the mobs are still alive and it just soft-locks the portal where it says 8 enemies but nothing is there and the portal expires when the timer ends

Found out after initial post it is because the light entity from the floodlight causes ISpawnInterdiction even when the light is pointed away from the mob spawning location making it hard to pintpoint and not make sense

The FloodLight is implemented by placing FakeLightBlockEntity which implement ISpawnInterdiction
I post this here for a reference
https://github.com/BluSunrize/ImmersiveEngineering/blob/51e5abdf2a1f9c650232678444850cf8605bb864/src/main/java/blusunrize/immersiveengineering/common/blocks/FakeLightBlock.java#L66
And the rule to predicate cancelling event is here
https://github.com/BluSunrize/ImmersiveEngineering/blob/1.21.1/src/main/java/blusunrize/immersiveengineering/common/util/SpawnInterdictionHandler.java#L96-L123

Since I haven't played IE, it was just now, I found this is configurable.