Looks like they might be trying to grow their mycelia network, for those that don’t know a mycelia network is like the roots of a tree but for mushrooms. Mycelia networks span almost entire forests, they are key to distributing nutrients and recent studies are showing that some trees communicate to their offspring through it.

I don’t know for certain, not an expert on the subject. This is my best guess.

Humidity is high enough the mycelium tried to branch. Reduce the humidity.