Email stops fetching

Every morning I check my email (gmail) on my 6+ and everything is fine. I go about my day and after some time the email stops fetching giving me this error message. I have not gone into the settings to change anything. Why is email fetching ok for a while and then it stops working out of the blue ?

Deleting the gmail account off the phone and setting it up again fixes the problem. But after a while it comes back again. It's extremely annoying to have the email stop working without any apparent reason.

Any clues as to what the issue may be?