Easy fix, rather than waiting for the replacement. Just fill it up with some ply bits and with the long brush fill in with epoxy or any bond agent, like gorilla glue, etc. Don't blame manufacturers, it is pilots responsibility to make sure the ARF models don't fall apart.
I have found similar problems with numerous ARF models over the years, I have covered few cavities and poured in pint of PVA , gave it a good gargel and shake, drained it out and let it dry, good as new, LOL.