<snip>
$ ip route
Default via 192.168.0.1 dev wlan0 proto static metric 600
10.0.0.0/8 dev rndis0 proto kernel scope link src 10.15.19.82
192.168.0.0/24 dev wlan0 proto kernel scope link src 192.168.0.71
192.168.0.0/24 dev wlan0 proto kernel scope link src 192.168.0.71 metric 600
so I've not got my gemini yet to be able to check, but I think I can see a problem for you there, which might explain the issue. You've got two interfaces (wlan0 and rndis0) . rndis0 has got a route to 10.0.0.0/8 which means that any traffic for addresses in that range (IIRC your captive portal was in the 10.x range?) will go over that interface, when presumably you're wanting it to go over the wlan0 interface.
In theory, you should be able to delete the route in question to see if that affects things (e.g.
https://serverfault.com/questions/181094/ho...-routing-table) , but I'm not sure without seeing a setup, why that route has been put in place...