When I click to active Custom Hostnames, it will always be loaded
May I ask if there is some error shown in the console of the Developer Tools (F12) at your Web browser?
May I ask have you tried using a different Web browser, or tried clearing your Web browser cache?
How about using a Private window (Incognito mode) or a VPN connection if possible?
Is it the same behaviour on your mobile phone (4G LTE, mobile data, cellular)?