Internal Server Error in PDF Services SDK - HTML to PDF

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This was working fine before, but I am now getting this error about 90% of the time. This is happening when converting HTML to PDF.

Our Code:

ExecutionContext executionContext = ExecutionContext.Create(credentials);
CreatePDFOperation htmlToPDFOperation = CreatePDFOperation.CreateNew();
FileRef source = FileRef.CreateFromStream(HTMLStream, "text/html");

htmlToPDFOperation.SetInput(source);
SetCustomOptions(htmlToPDFOperation);
FileRef result = htmlToPDFOperation.Execute(executionContext);

Stack Trace:

Adobe.PDFServicesSDK.exception.ServiceApiException
HResult=0x80131500
Message=An Internal Server Error has occurred.; transactionId=sXvaanS7qCYgrgwctjw9XqJui9SIdCqr
Source=Adobe.PDFServicesSDK
StackTrace:
at Adobe.PDFServicesSDK.core.http.HttpClient.CheckCPFContentReponseStatusCode(CPFContentAnalyzerResponse cpfContentAnalyzerResponse, String requestId)
at Adobe.PDFServicesSDK.core.http.HttpClient.ExecuteRequest[T](HttpBaseRequest baseRequest)
at Polly.Policy`1.<>c__DisplayClass11_0.<Execute>b__0(Context ctx, CancellationToken ct)
at Polly.Retry.RetryEngine.Implementation[TResult](Func`3 action, Context context, CancellationToken cancellationToken, ExceptionPredicates shouldRetryExceptionPredicates, ResultPredicates`1 shouldRetryResultPredicates, Action`4 onRetry, Int32 permittedRetryCount, IEnumerable`1 sleepDurationsEnumerable, Func`4 sleepDurationProvider)
at Polly.Retry.RetryPolicy`1.Implementation(Func`3 action, Context context, CancellationToken cancellationToken)
at Polly.Policy`1.Execute(Func`3 action, Context context, CancellationToken cancellationToken)
at Adobe.PDFServicesSDK.core.api.CPFApi.CPFStatusApi[T](InternalExecutionContext context, String location, String targetFormatExtension)
at Adobe.PDFServicesSDK.core.api.FileDownloadApi.DownloadFile[T](InternalExecutionContext context, String location, String targetFormatExtension)
at Adobe.PDFServicesSDK.pdfops.CreatePDFOperation.Execute(ExecutionContext context)