About PDFNET-45498, we are afraid there is not any update at the moment. This ticket has been logged recently and may take some months to resolve. Please be patient and spare us little time.
Moreover, would you please elaborate if you have tried to work with Aspose.PDF for .NET API or with Adobe Acrobat. If you are working with the API then please share code snippet and the files for our reference.
Furthermore, please create a separate topic while sharing respective details and files for which alt text is missing, so that we may investigate it in our environment.