Production Application Crashes when accessing X509Certificate2 Key Data

Really hoping you can help me with the following.

I have created an .Net Core Application that is run as a windows service. I'm trying to open a certificate in order to decrypt the app settings.

The certificate I am using on my local machine and the test server is the same certificate. The Public key for the certificate in question is an X5092.

I have the following code to read the Certificate from the store to get the values.

public void Start()
{
    using (var store = new X509Store(Location))
    {
        store.Open(OpenFlags.ReadOnly);

        var signingCert = store.Certificates.Find(CriteriaType, _thumb, false);

        _logger.Warning($"Number of certs found {signingCert.Count}");

        var firstCert = signingCert[0];

        _logger.Warning($"Subject - {firstCert.Subject}");
        Thread.Sleep(1000);
        try
        {
            _logger.Warning($"Private Key - {firstCert.PrivateKey}");
            _logger.Warning($"Get RSA Private Key Method {firstCert.GetRSAPrivateKey()}");
        }
        catch (Exception ex)
        {
            _logger.Error(ex.ToString());
        }
    }
}

The application finds the certificate using the ThumbPrint enum, the thumbprint and doesn't care if the certificate is valid or not. The value of firstCert is the cert I am after. The "Subject" prints to the log file correctly as well as any of the other props apart from the Public and Private Key props.

My application crashes as soon as I call any of the following

firstCert.PrivateKey
firstCert.GetRSAPrivateKey()
firstCert.PublicKey.{anotherProp}

The crashes happen under the following conditions.

1. The server is rebooting.
2. The application is set to automatic start up.
3. The application is run as a service.
4. The Logon is Local System Account. When the application does crash, there are no logs after I try to access key data of the cert. No exception caught, the application fails to start, I only find this out by looking at the services to which is says stopped.

The application works correctly in the following conditions

1. When debugging on my local machine.
2. Running as a service, on automatic start, as the Local System Account on my local machine.
3. As above but started from the services feature.
4. On the test server but with a delayed start up.
5. On the test server but started from the services feature.

The app written is .Net5 My local machine is windows 10 enterprise. The server is 2012 R2.