It seems to be known: https://community.qlik.com/t5/New-to-Qlik-Community/Unable-to-add-qvf-files-as-an-attachment/m-p/150...
Yes, this is a known issue for us. We've set the system up according to the "rules and settings" that should enable this to be possible, but for some reason it doesn't work.
So we have an open ticket with the vendor to try and solve this issue. I know we asked for an update on Friday so hopefully this can get solved soon.
In the meantime, please zip the files before uploading them as that should be a possible workaround.
Thank you for your patience.
All the best