issue when using IMAP through iPhone

The issue has happened to me many times, but not all the time. And it only happens when I'm using it from my iphone (using IMAP).

When I open my zoho inbox, when there are emails with attachments, my inbox will try to retrieve these emails, then these emails appear/disappear. It keeps doing this in a loop, never end. If I try to quickly open the email as soon as it appears, then it actually opens a different email.

This is very frustrating. And it only happens when I'm using it through my iPhone, not from the actual webmail. Therefore I think it's gotta do with the IMAP. It's very inconsistent. Because of this issue, I don't really use my zoho mail anymore.