Aipad air 7.1.2 won't open some attachments on the mail app. Sometimes when hit the "download full attachment" long messages even simply disappear from the e-mail

Some e- mail attachments won't open on my iPad Air w/ 7.1.2., some does. There is this sort of link on the bottom of the e-mails that says "download full attachment " and when pressed sometimes the attachment opens but sometimes it simply disappear from the e-mail. I couldn't identify the problem neither solve it. Could somebody help me please