Lichborn Exiles Not Spawning

In the past few days I have run at least 20 overrun by abyss maps, with around 250~350% increased chance for rogue exiles on every single one.

Out of all of them only a single map spawned a rogue exile, and that exile did not respawn as lichborn despite being literally on top of an abyss.

How many of these maps am I going to need to play to get a single heart of the well diamond? Is something wrong with these mechanics somehow?

I just don't get how I can have 300% increased chance of rogue exiles, and map after map they don't spawn. Much less spawn in the correct situation to provide a diamond. Even the one that appeared to be in the correct situation didn't work as expected.

And now I've pretty much used up all the overrun nodes on my atlas.. I wanted to experience this mechanic at least once instead of buying the item on the market.