Using an up-to-date version from github master, my mu4e is perfectly able to verify PGP/MIME signed emails, but fails to decrypt PGP/MIME encrypted emails. It simply shows that there are two attachments (this is to be expected for PGP/MIME), but it doesn't make any further attempt at decryption.
Is there anyone else on the list that perhaps knows of a work-around or a fix for this? At the moment, I do "M-x epa-mail-decrypt" in the raw email view to be able to read the decrypted version, but this has a number of limitations.