doveadm client not compatible with this server (mixed old and new binaries?)

[Kevin Golding]

I'm getting the error "doveadm(10.0.0.10): Error: ddoveadm client not  
compatible with this server (mixed old and new binaries?)" on the source  
server (10.0.05) when trying to sync with a new destination server and I  
feel the error seems very obvious and self-explanatory except for one  
small thing - both servers claim to be the same version

dovecot -n reports:

Source (10.0.0.5):
# 2.2.31 (65cde28): /usr/local/etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.19 (e5c7051)
# OS: FreeBSD 11.1-RELEASE-p1 amd64

Destination (10.0.0.10):
# 2.2.31 (65cde28): /usr/local/etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.19 (e5c7051)
# OS: FreeBSD 11.1-RELEASE-p1 amd64

The only difference between the two outputs of dovecot -n are the  
mail_replica host (which are set to each other) and the ssl_cert location  
(which have their own domain names in the path).

Replication is set to use tcp and the ports and passwords match. I was  
wondering if it's something they may depend on but the ones I'm aware  
cause most problems in general (libressl-2.5.5 and maridb-client-10.1.26)  
match. Any pointers that can be offered would be appreciated because I  
feel I'm missing something obvious.

TIA
Kevin