Regression: Certificate validation does no longer work on linux machines when upgrading from 3.0.6 to 3.0.7 or 3.0.8

I used to build an instance of IMqttClientOptions as follows:

private IMqttClientOptions GetConnectOptions()
{
    var builder = new MqttClientOptionsBuilder()
        .WithCleanSession()
        .WithTcpServer(Configuration.Host, Configuration.Port)
        .WithProtocolVersion(MqttProtocolVersion.V311);

    if (Configuration.Auth.Enable)
    {
        builder.WithCredentials(Configuration.Auth.Username, Configuration.Auth.Password);
    }

    if (Configuration.Ssl.Enable)
    {
        builder.WithTls(parameters =>
        {
            parameters.UseTls = true;
            parameters.AllowUntrustedCertificates = Configuration.Ssl.AllowUntrustedCertificates;
        });
    }
            
    return builder.Build();
}

This used to work fine, also for ssl connections with letsencrypt certificates and AllowUntrustedCertificates=false. By bumping the version to 3.0.7 or newer it still works on windows. It doesn’t on a linux (ubuntu bionic) machine where it fails with the error message The remote certificate is invalid according to the validation procedure..

[dpsenner]

Bumping the application from netcoreapp2.2 to netcoreapp3.1 resolves the problem.

[chkr1011]

I assume this issue is solved with the upgrade to netcoreapp3.1.