If debug logging is active, with every session dovecot tries to open files in /proc Oct 17 18:47:15 imap(user-x)<90451><kJll...i>: Debug: open(/proc/self/stat) failed: No such file or directory Oct 17 18:47:15 imap(user-x)<90451><kJll...i>: Debug: open(/proc/self/io) failed: No such file or directory As i understand "self" references to the process self. But that seems not to be the case in FreeBSD? I also find no reference to this in config files.... Searching for a way to change path, disable, whatever...
Maybe on FreeBSD the analogue of "self" would be "curproc". Analogue of "stat" would be "status". Analogue of "io" unknown. It's probably from the original dovecot developer. These are just my guesses, maybe they will help in some way.
I've asked on the Dovecot mailing list (which has the upstream developers) about this.