I'm proposing an explanation for phenomenon "A". Other folks say "No need! We already have an explanation for phenomenon A, it's a natural consequence of phenomenon B". Problem is, phenomenon B is also unexplained. I want to call this out in a polite but firm way.
I've thought of:
This pushes the question off onto unexplained "B"
This is merely shifting the burden of explanation.
This is probably a logical fallacy with a Name and Employment History, but I can't think what it is. Any thoughts?