It sounds like you might be trying to tackle too much all at once (Unraid + Docker + Syncthing are a lot of moving parts).
There are so many different ways to set things up so I recommend checking out the following guides in Unraid’s wiki:
There are multiple Syncthing container images available. You didn’t mention which one you’ve using, but the official one and the one from LinuxServer.io are both excellent choices.
A few previous posts on this forum that might also be of help: