it is posted in gmail known issues. I am sorry, it is a problem of gmail.
if you expand pop, imap & sync, then you have the following and you can report the issue (I have also done it).
'imap.gmail.com is not responding' error when retrieving mail via IMAP, mobile device, or tablet
We are aware of an issue where users are receiving an error that '"imap.gmail.com" is not responding' when using IMAP on their computers, mobile devices, or tablets. We are currently working on resolving this issue.
In the meantime, you can sign in to Gmail through a web browser. For Android and iOS users, you can also download the Gmail application in the interim.