I came across something like this and choked it up to a immature puffball. It was frowning inside a crack about 4’ off the flare on a bigleaf maple. Oddly right above some old ganoderma FBs, slightly above that last years old dried up puff ball. It was literally about the texture of a marshmallow. I only took a video, so can’t post it here.Well that's just good old fashioned gross.
If not a mold, how about an odd bacterial flux of some kind?