Running:
grep "^UID_M" /etc/login.defs
Returns this:
UID_MIN 1000
UID_MAX 60000
My old sddm conf file had a few lines to increase the max UID, Im told that systemd-homed users are outside that range.
Entering the following into /etc/plasmalogin.conf has not helped:
[Users]
MaximumUid=60513
MaximumUid=1000
I suspect this might be the problem.