We are really sorry for the impact to some customers caused earlier this week by a failed software update.
This was caused by a software update on the core imap handlers on the platform, which had an unexpected side effect causing some Apple IOS clients to redownload the contents of a folder repeatedly. The issue was resolved by a rollback within approximately 5 hours of the release going live.
We are reviewing the testing methodology and post live checks to ensure this does not happen again.
Thanks for the update @RobbieMac
To clarify also and to help with your investigations, I first had the issue around Thursday 9th July so wasn't new to the 13th/14th July...so maybe some other patch caused the issue.
The problem has not occurred since, but as it was an intermittent problem it was difficult to know whether this was a result of a fix or not. It’s good to know the fix has been applied and what the cause was, thanks.