Bacteria need air (aerobic) to breakdown organic matter. Where they convert nitrogen from the air to the roots of the plant (Air is 78% nitrogen)
Fungi don't need air (anaerobic) That's why you seen my fungi in the forest.
I would probably aerate your yard soon, that should help with the fungi.
If that doesn't solve your problem, then use some type of de-thatcher to get the thatch off the surface of the ground. Then apply some type of microbial stimulant (organic fertilizer)
Then keep on mulching, Mulching your yard can add an additional 120 lbs per acre of free nitrogen (as long as you have bacterial activity)