[Exim] Failed to open waitremotedb

This failure periodically shows up in my syslog:

/var/spool/exim/wait-remote_smtp: invalid argument

Could someone help resolve this?

FYI: I am running 3.22 on Debian Potato. The .deb for this distribution
come with 3.12; however, I downloaded the tar and compiled / installed
it.

Thank you.