My friends' PGP messages keep turning up empty

I’m in contact with a friend of mine, regularly through PGP-encrypted emails.
While they can decrypt and read my emails just fine, lately whenever I decrypt their messages they turn up empty so we’ve been trying to get to the bottom of it together but couldn’t find a solution.

I use Claws Mail whereas my friend uses Proton Mail, although we both use the Linux terminal to encrypt our messages.

Any help?

Hi Jack,

so you are using gpg from Gpg4win on the command line.

Try a decrypting command with verbose output like

gpg -vv --decrypt yourfile

(There are even more options to get more output. If the resulting file is indeed empty, it will be a problem on the senders side.)