A similar issue was reported to the B2C team.
One resolution was to remove the default host header in Azure Front Door backend pool. If your requests have x-forwarded-for headers, you can try disabling that with:
options.ForwardedHeaders = ForwardedHeaders.XForwardedHost | ForwardedHeaders.XForwardedProto;
For the full troubleshooting, see: https://github.com/AzureAD/microsoft-identity-web/wiki/Deploying-Web-apps-to-App-services-as-Linux-containers
And: https://github.com/AzureAD/microsoft-identity-web/issues/1076