Q: Email attachments do not show in iOS 9.3.5 mail app

On my iPhone 6 (9.3.5) the mail app does not show the attachments. The paper clip icon is there, but when I open the mails there is just a white space instead of the icon that can be clicked to view the attachment.

On my iPad Air (9.3.2) the exact same emails in the same mail account work just fine. This obviously hints at a problem of iOS after 9.3.2. I deleted the mail account, set it up again - but the problem stays the same.

Any hints what I could do to fix the problem?

thanks!