The lecithin in the egg yolk helps bind the flours together in a natural way, helping the natural gumminess of the oats stick the muffin crumb together. (eatthelove.com)
Maybe I will add some almond flour instead of more cassava to see if it helps with gumminess. (predominantlypaleo.com)
It has a tangy flavor and natural gumminess when processed. (bonappetit.com)