Hi! really don't know if it's a bug or just not mentioned, but I was able to fix it by simply closing the mycelium. It seems that mushrooms only dry out if they are outdoors. So closing the cave to count as an interior worked to prevent them from dying.

I have altered the drying message to now say that they are dying due to high temperature, so it should now be more clear what's going on.

Ah, thank you!

Hi! I noticed they die if their put on 'Mycelial Soil', and they don't if planted on 'Fungal Garden Gravel'! Hope this helps anyone else who was confused as I was!