How does "Rare Anomaly Detected" and "High Level Anomaly Detected" actually work?
Is it
When the notification trigger, Random encounter has a chance to be Rare / High Level Anomaly
OR
I've to find a tile in the current Room/Floor close to where the notification trigger to trigger a Random / High Level encounter?
The latter is because I noticed that the same notification can trigger multiple time when exploring the same Room/Floor
If you go to some bar, one of the customers tells you that during either new abraxas or full moon abraxas has different enemies of spawning.
When you get the notification, I'm pretty sure that is when the rare enemy is now in the enemy pool.
Therefore, you have to be lucky to get the rare encounter, because you can still get normal encounters during that period.