I experience the exact same issue with a Synology NAS DS1515+ with 16GB memory. i also run on feralhosting, and have static ip, i know reroute can help out some times, but my speed is stuck on 500kb-1MB and after a restart i reach 36MB/s and Max out the full speed of my internet connection.
on Synology its possible to setup a task schedule to restart the sync app, but would like to know the root cause of this.
i have set my NAS to static IP and forwarded the BT Sync ports, and made direct connection.
Maybe the issue can come from Feral changing ip or ports of the sync! so it loose direct connection, don't know where to troubleshoot further to find out what is causing this
I don't know where to determine if the connection is direct, and how the feralhosting has been setup for UPNP on the hardware site,