I managed to get this to sync with my devices perfectly over LAN using the info I provided below.
But I still have one problem. I am unable to directly add a file to a folder via Windows Explorer on my SMB share. That is, I cannot drag and drop a photo into the
//Server/Storage/sync/My_Folder directory to be sent to my other devices. It says "permission denied" in Windows. How do I fix this?
Just letting you guys know. I had to swap my interface from "Bridge" to "br0" for this to work properly. Otherwise I also got the issue with it not connecting ever again after 15 mins. Also disabled the relay on all of my devices to first properly work out the LAN issues I was having, because if after a certain time a LAN connection can't be made it'll just move to using a relay and it's sort of hard to work out if it's using the relay (gotta scour the log, or look at the slow speed etc). In addition to that I added the port "22010" to the port mappings before installing the Docker app. Then I changed the listen address in the app to "TCP 22010" because having it set as "default" causes a "connected to myself, not supposed to happen" error every 60 seconds.
Then I set the listen address on each of my devices as follows TCP 22011, 22012 etc. and port forwarded these over my router. Not sure if I had to do these 2 steps but I did it anyway.
After this I re-enabled the relay so my files can sync when I am away from home. Over LAN I'm able to get just up to 50MB/s transfer speeds (Smartphone is the bottleneck) which is much, much higher than Nextcloud which used to only get me about 10MB/s. Probably due to less overhead and not having to write to a DB etc.
Hope this helps someone and thanks for providing this app.