Adobe Acrobat Reader DC: File upload to Adobe Sign not working

Hi.

I try to upload a 60KB PDF file to Adobe sign (free version with 1 transction left)

After selecting the recipients of the document the upload starts but it always hangs at about 70%

I don't get any error messages. Acrobat Reader DC Build 21.11.20039.0

Does anyone have an idea how to fix that?

Thanks,

Dirk