we have solved the problem by upgrading from Debian 9 to Debian 10... Somehow this solved all the problem, we did not change anything, everything else stayed the same version (node/npm/NodeBB)... FYI...
It was already dump.rdb so I left it that way. Restarted redis and still no forum.
Could the directory structure be at fault? I didn't have the new redis at the location you pointed to, it was at /var/lib/redis/redis-2.8.9. (both redis.conf files point at dump.rdb by the way).
EDIT: It's back now! You da' man. I'm still not sure which is the real redis.conf file though.
