hi Vinod,
sorry to hear u're stuck with the login page issue...
check if azure ad b2c itself is having a hiccup. microsoft's service health dashboard is the go to place for that. just peek at https://status.azure.com/en-us/status and look for any active incidents under azure active directory or azure ad b2c. sometimes it's just a cloud thing and they're already on it ))
if the dashboard shows all green, then its time to look at your app service. open the azure portal, head to your app service, and check the 'diagnose and solve problems' blade. run the availability test there. it's like giving your app a quick health checkup ) https://docs.microsoft.com/en-us/azure/app-service/overview-diagnostics
also, while u're there, glance at the app service logs. sometimes the answer is hiding in plain sight. u can enable application logging if its not on already https://docs.microsoft.com/en-us/azure/app-service/troubleshoot-diagnostic-logs
try accessing your app from a different network or device. sometimes its just a local network gremlin causing trouble. worth looking into ))
clear browser cache or try incognito mode. sounds simple but u'd be surprised how often it works ))
if u're still hitting a wall, check your ad b2c configuration. maybe the custom policies took a coffee break https://docs.microsoft.com/en-us/azure/active-directory-b2c/troubleshoot and don't forget to verify your app service authentication settings. if azure ad b2c integration got misconfigured, that could block the login page https://docs.microsoft.com/en-us/azure/app-service/configure-authentication-provider-aad
for anything deeper, u might need to check application insights if u have it set up. the traces there can be super helpful. microsoft made it pretty straightforward https://docs.microsoft.com/en-us/azure/azure-monitor/app/asp-net-troubleshoot-no-data
as well check this sometimes scaling up your app service plan for a minute can shake loose whatever's stuck. azure's autoscaling is cool but occasionally needs a nudge )
last thing if u recently made changes to your ad b2c tenant or app registrations, double check those settings. one wrong redirect uri can ruin the party https://docs.microsoft.com/en-us/azure/active-directory-b2c/application-types
hope this helps vinod )) let us know how it goes
rgds,
Alex