B One running Filemaker server, repeated drop outs

Hi, I have just installed a Peplink B One in our small business,
running latest firmware 8.5.0.
Has a Telstra Gateway Pro as modem to NBN (unable to use bridge mode), so Telstra still has DHCP enabled and using port one to feed wan 1 on Peplink.
we run Claris filemaker as our business software, and my computer is running the server, 3 computers (all macs) on the network normally connect to my Mac, which has a wired connection to port one on the Peplink, with access to any VLan. other computers are either on wifi to peplink or a second Access Point on other side of building.
I am having issues with my own access to the server, which is running on my computer, since the Peplink install,it randomly loses its connection every few minutes for a second or two. I have disconnected my computer from the wifi, set a dhcp reservation on the peplink for my mac, and re added the host server settings in filemaker, but still seems to be happening. any ideas?
is the Telstra setup ok or do I need to disable DHCP on this unit? Wifi is off and only device connected is the Peplink

What do you see if you do a continuous ping to the server from the client devices?
Possible network loop?

On your computer that is running Filemaker Server are you also running FIlemaker client or are you only running FM Server and all clients are the other 3 Macs? Do all clients have the same dropout? Are all Macs on WiFi? Do you have any options to use Ethernet to rule out WiFi as the issue? What did you use before the B One and did you have any issues? If you have the option to disable DHCP on the Telstra, I would disable and let the B One handle DHCP (otherwise you get double NAT).

have put server mac on ethernet only with wifi off and issue seems to have gone away.
yes server mac is also running a client.
i’m not really sure about the double NAT bit, and I am now having issues with a remote computer accessing the server remotely, and wonder if thats the issue.
so i just disable dhcp and assign a fixed IP/address reservation?
do i still need to port forward on the telstra for Filemaker server?
have port forwarded port 5003 on tcp and udp and set firewall rules similar on Peplink, but still can’t access remotely.
The Telstra used to work fine, internally and remotely, but I may have removed the port forwarding from that when I changed to this set up. will check today.

how does a network loop show up?

Generally solid or very fast blinking lights on the ports, or port errors if you have a managed switch.