Frankly I was beginning to think the only systems it did work on were Debian systems. In any case you have nothing to lose. Try this:
sudo apt install memcached python-memcache
sudo service memcached restart
Check /etc/memcached.conf. You might want to add the IP address of the server to the -l line, like so,
-l 127.0.0.1,{your_server_IP_address}
Stop and restart Seafile before and after installation of the above. I think the third configuration will work (fingers crossed…).
Let me know what you see. We really need to figure out what’s missing from the installation docs. There are far too many posts on this issue.
-Thanks!