Having the same problem for a month now. Random clients are disconnected every 5-30 minutes. Server logs "Client no longer responding, connection closed. (10)"
We have tried moving servers to a new VM, moving VM to a new physical server, moved switches, installed completely new servers. The problem is now happening to three different servers using two FileMaker Server versions (13 and 15).
Clients disconnecting are physical machines, virtual machines, remote desktop connections using Windows 7, 8, and 10. A physical machine can have a connection to the hosted file at the same time as a virtual machine running on the same physical machine. Virtual machine will disconnect without the physical machine disconnecting.
Sniffing packets show that the FileMaker server will send a transmission to the client, the client will respond, the server sends a retransmission, then sends a disconnect.
There is no latency or server performance issues that we can see. It just seems like the FM server is not seeing the client acknowledgements.