Well, I just googled honey fungus and all thr references were from the UK. Is that where you live? Anyway, it looks to be aggressive and sometimes lethal. I'd repot ASAP in some good quality soil (wash the roots, spray with fungicide), and return the bag of compost to where you bought it. I had a 'mushrooms in the philodendron' problem a while ago and used a commercial houseplant fungicide with good results, but those yellow mushrooms were just finishing up with the cheap potting soil I got, and not eating the live plants. Good luck!