Re-Agreeing to public WiFi through login screens
This sounds like your iOS device may have some sort of ban on the network. From experience, you can set suspicious devices to be auto-banned. This is especially common on public networks. I would imagine that iOS tried to Auto-Join too many times and the network may think it is a DDoS attack. I suggest you talk to the transport company on why you aren't connecting to the internet. Of course, this isn't something that just everyone will be looking to talk to a transport company and I understand it's inconvenient, but I've run a network in the past that's public and that's basically how it works.
EDIT: The image shows our set duration of invalid attempts. We have set our network to ban the device for 15 minutes, although there are options to ban the device permanently (strictly that only administrators can unblock the device). These systems may vary, but work similarly.