mmap() Error, Invalid Argument - Double slash in path?

I get a ton of these mmap() errors in the log. I noticed there's a double slash before Maildir. Is this normal? Config error? Dovecot bug?

dovecot: imap(email@email.net): Error: mmap() failed with file /shares/email/vmail/vmail1/email.net/e/m/a/email-2017.02.25.08.09.39//Maildir/dovecot.index.cache: Invalid argument

I'm running dovecot version 2.2.22

Thanks Eric