PDF doesn't download in iPhone mail

Sometimes after receiving an email with a pdf attachment in mail, it cannot be downloaded. When I press on the pdf, it shows the black download arrow, but it doesn't download. It goes back to "tap to download".

When I forward this email on my laptop to my hotmail address and open it in that account on iPhone mail, I can download the same pdf and open it on the iPhone.

Also when using webmail through Safari, I can download and open the pdf.

So there is no issue with the pdf. There seems to be an issue with mail sometimes not properly dealing with (pdf) attachments. Is there a fix for this (other than going to my laptop or webmail)?

Thanks.