I've been making men's shirts for years, and the rule I follow is, if you are going to wash it, don't use fusible interfacing.
I"ve tried every brand, different iron settings, steam, no steam, teflon plates, an iron with no steam holes, everything. Inevitably, once it goes into the wash, it's ruined.
But so what? Professional shirtmakers don't use fusibles either. Muslin or self interfacing works just fine.