What you say is very interesting.
Please don't misunderstand - I was not suggesting any fault within your extension. Whilst WhatsApp is not ideal I'm very glad to have some method for exporting multiple attachments and am sure the problem lies within my phone, its apps or the Android version. That may become clearer from any feedback from other users.
Look forward to any developments you come up with. I'm happy to test if that would assist.
Thanks again for your fast and helpful responses,