I concur with what the others have written about damp soil. Mushroom presence also suggests soil that has been contaminated with fungus spores. Not a problem necessarily, but peat-based sterile potting mixes don't normally have this problem. Be on the alert for fungus gnats that are also introduced in non-sterile potting mixes and also thrive in damp soil. I suggest that you remove all loose soil, including the mushrooms and their fine root systems, from the surface of the pot. Allow the soil to dry deeper into the pot between waterings. Arboricolas are reasonably drought tolerant. Warm temps and good air circulation will help discourage fungi.
