RT-AC3200 Wired D/L limited to 50 mpbs on 250 mbps connection

I used to have a 50 mbps connection till recently so did not notice this issue. I have the RT-AC3200 setup behind the ISP modem which in turn is behind the ISP fibre ONT. If I connect my laptop directly to the ISP modem, using SpeedTest.Net I consistently get the 250 mbps speeds. I tried this with 2 different ethernet cables to test both those cables (one of which is normally the one connecting my RT-AC3200 to the ISP Modem). When I connect my laptop to the RT-AC3200 using the same cable and...

RT-AC3200 Wired D/L limited to 50 mpbs on 250 mbps connection