Because access to the resource (URL) is blocked (see the explanation on your tablets screen). Most likely reason is the firewall on your PC. Please check the firewall settings there:
Thanks. My tablet and phone have no problem connecting the WiiM Remote Android app to my core running on a Windows 10 computer. So I think I should be all right with my firewall settings.
Would there be a firewall setting specific to the Roon display URL?
IDK what you want to tell us by this or what the “WiiM Remote Android” even has to do with all this?
Does the tablet that can’t connect to the web display run Roon Remote? If so, then probably use the Roon Remote app instead. If not then you have to figure out what blocks the offending tablet from accessing the Roon Server web service running on your Windows 10 computer.
Remote diagnosis of your network is hard to do. If you need help, please share more details about your network setup.
PS: The IP-Addresses used in a home network are typically already private, so there is no need to black them out in your screenshots. Omitting information may make it impossible for others to help you resolve your issue.
Update:
If the IP-Address yo used is 127.0.0.1 then please replace it with the actual IP-Address of the Windows 10 computer when you try to connect from the tablet.
I’m now at a different home with my laptop running Roon Core. Web Display works fine here. I’ll check again when I’m back on the other network at the end of this week.