Fermentation

It looks like you have some air pockets in your mass. The aspergillus will keep making white filaments where ever there is a surface with a little oxygen present. If it is anything other, it will not survive competition with the aspergillus in the environment created by the miso so it will not survive mixing it in. There are few fungii capable of making you sick whilst also able to grow in the miso, and even then it's usually because of mycotoxins produced as a side product from the metabolic processes. This means they would have to be present in a very large amount, which inevitably makes the whole thing very easy to detect by smell and taste. Mix it in, and once the ferment is supposed to be completed, if it smells and tastes off, throw it out. But, I think more often than not you'll end up fine.

Side note, it's only since recent times people started fermenting in glass jars where everything is visible. Traditionally smell and taste were the only markers people used. Trust your senses!

Happy fermenting!