GL-MT300N-V2 Mango very slow on public wi-fi

I have my Mango mini router wirelessly connected to a high-speed public wi-fi network (100+ Mbps when directly connected), but I’m only getting speeds of 1-2 Mbps on my devices that are connected to the Mango’s wi-fi network. Any ideas why the huge loss of speed?

I have good signal strength from both the public wi-fi point and the Mango, and I’ve tried connecting my laptop to the Mango with an ethernet cable, but still get on 2-3 Mbps.

I’ve left all settings on default values except for disabling DNS Rebinding Attack Protection so I can access the public wi-fi’s captive portal page. I’ve also upgraded the firmware to 3.102.

Usually you should get 20+mbps when using repeater.

I do know some cases that speed is low but I have no idea. Seems some network does know you are connecting a router and tries to throttle it.