If iperf tests or even the OpenSpeedTest (which I don't use anymore as it has a bug) report full 900/900 then there isn't likely an issue with the flint 2, it would be odd to see a different region getting slower speeds, if speeds are slower and repeatedly slower on certain servers then that would suggest that the servers dont have the bandwidth to saturate your line.
You could check your MTU settings and compare settings from your old router. Also try with hardware acceleration off to see if anything changes.
Regarding the bug on the OpeSpeedTest local docker (maybe the windows client too), if you test via Firefox you will notice that the upload speeds are not true, iperf is the best way to test.
You can run the iperf server from the glinet plugins and connect your laptop to it as a client to test.