Hi,
I also experienced this when I was running Sierra so I don't think it is specifically related to High Sierra.
I now understand that our problem may be that our Macs are remembering the network and settings.. When we go back and try to connect it is "holding" the settings from the last time but the router has already cleared us out.
The below may work:
Resetting your computer clears the cache and now forces your computer to request a new ip address instead of trying to use the last ip and settings it had when on the network.
A quicker and easier fix that might work would to open your system preferences -> network -> advanced -> TCP/IP tab and click "Renew DHCP Lease". That will force your computer to request a new ip address.
I have personally found clicking on the WiFi icon, opening network preferences and then running diagnostics usually then forces the WiFi login/pop-up page to appear.
Not sure why iOS devices seem better at handling public Wifi (other than I guess more likely to come into contact more frequently) than MacOs though.