Delirium Scarab of Delusions

So I'm trying out this Scarab and in some maps there's still maps without layers of Delirium dropping and so far I can't figure out why.

Is there some mechanics where the scarab doesn't work? The last map for example I got 4 maps with and 7 maps without delirium dropping. That's very unusual but still, don't know why.

Other scarabs I'm using are Cartography Scarab of Escalation, Cartography Scarab of Corruption and Cartography Scarab of Multitude. Got no Mechanics other than Shrines specced into my Atlas, but alot of times I get Rituals inside the maps.

Usually I get 100% maps with Delirium layers, so the last map was definitely an outlier.

/edit: I think I figured it out. I didn't check the delirium rewards of that map, but I'm sure it was maps. So that's probably where the Scarab didn't work. Those 7 maps came from delirium rewards rather than drops.