iOS download does not work for some

For papers with PDF files, downloading on iOS sometimes starts normally, but the button quickly turns into an exclamation mark inside a circle. There is no message telling me why it doesn’t work, but the Chrome app works fine with these papers, and for entries without a PDF attached, the download button on iOS also works fine. Any suggestions?

Can you contact our support team via the in app-messenger. We would need to look into your logs to see what’s going wrong here.