@Anthony_G I used to have a similar setup using AX55 routers. Most (if not all) Tp-Link routers can be used in Wireless Router mode or in Access Point mode. As you already have your router in AP...

@Marvin_S Thanks for responding. After a day, the speed has not dropped. It would appear that there is a problem with the WAN/LAN port speed negotiation which the engineers should look at. The MR500...

Update: Changing the MR500 cable connection from the WAN/LAN port to one of the other LAN ports fixed the problem.

I recently discovered that the MR500 LAN connection to my main router has dropped to 100 Mbps instead of its normal 1 Gbps. The MR500 is being used as a secondary internet connection in a failover...

@Dip_sbmc I would connect a portable computer (capable of 1000 Mbps) directly to the ISP box and see what the connection speed is.

@Dip_sbmc What is the WAN port connected to? It would appear that you are connected to a 100 Mbps source.