I suspect this is an early stage in the development of one of the shelf-like or bracket-like polypores - possibly a species of Ganoderma. These start out as a featureless, hemispherical blob that eventually differentiates into markedly different upper and lower sides. In one photo you see the pored underside beginning to develop. If it is a Ganoderma the upper side will eventually become brown. The full development can take a long time. If you go past this point often you might want to look at this fungus in a month's time, two month's time...etc