Android Devices running Android 13 and earlier cannot reach backend due to SSL issues after migrating backend firewall to Cloudflare. Any ideas?

Over the weekend we migrated our firewall and security to Cloudflare. Ever since, on Android devices running Android OS 13 or older, requests to the backend from my Xamarin Forms app drop immediately. Switching networks, uninstall/ reinstall, and restarting device does not help.

Upon sending the request, it throws a System.Net.HttpException with the message “the SSL connection could not be established, see inner exception. Full stack trace below.

System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception. --->   System.Security.Authentication.AuthenticationException: Authentication failed, see inner exception. --->   Mono.Btls.MonoBtlsException: Ssl error:1000007d:SSL routines:OPENSSL_internal:CERTIFICATE_VERIFY_FAILED   at /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/external/boringssl/ssl/handshake_client.c:1132   at Mono.Btls.MonoBtlsContext.ProcessHandshake () [0x00042] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/System/Mono.Btls/MonoBtlsContext.cs:220   at Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake (Mono.Net.Security.AsyncOperationStatus status, System.Boolean renegotiate) [0x000da] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/System/Mono.Net.Security/MobileAuthenticatedStream.cs:715   at (wrapper remoting-invoke-with-check) Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake(Mono.Net.Security.AsyncOperationStatus,bool)   at Mono.Net.Security.AsyncHandshakeRequest.Run (Mono.Net.Security.AsyncOperationStatus status) [0x00000] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/System/Mono.Net.Security/AsyncProtocolRequest.cs:289   at Mono.Net.Security.AsyncProtocolRequest.ProcessOperation (System.Threading.CancellationToken cancellationToken) [0x000fc] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/System/Mono.Net.Security/AsyncProtocolRequest.cs:223    --- End of inner exception stack trace ---   at Mono.Net.Security.MobileAuthenticatedStream.ProcessAuthentication (System.Boolean runSynchronously, Mono.Net.Security.MonoSslAuthenticationOptions options, System.Threading.CancellationToken cancellationToken) [0x0025c] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/System/Mono.Net.Security/MobileAuthenticatedStream.cs:310   at System.Net.Http.ConnectHelper.EstablishSslConnectionAsyncCore (System.IO.Stream stream, System.Net.Security.SslClientAuthenticationOptions sslOptions, System.Threading.CancellationToken cancellationToken) [0x0007b] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/external/corefx/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs:165    --- End of inner exception stack trace ---