I found fleet to beat...



but when battle begun efect was different than expected.

I found 125 scavengers as expected and 124 scourges. So my fleet was gone... in seconds

https://xcraft.net/battle/index.php?battle_id=52e78ea5594e6c38941bde264d96c2cd

But on map scourges wasn't present. Also it wasnt in simulation.

sounds ok, scourges have ability called "Coordinate mining" with following description:
While holding on space coordinates Scourges will release a gas cloud that cloaks them from common space scanners. This allows them to stay there invisible to galaxy radars, so enemy won't see Scourges among the fleet units while attacking the coordinates or viewing the galaxy.
How to counter:
1) Reconnaissance-in-force. You can send a small fleet that will show full enemy composition if it enters the battle.
2) Sensor Phalanx can show you full composition of any fleet.

"Nice" 
Thank You for information.

"Sensor Phalanx can show you full composition of any fleet." -- baloney