net::ERR_CONNECTION_TIMED_OUT
Since you are not facing any connection issues, this toast message, on the face of it looks not related to connection . 

As a first step, install toaster and notification history to find out the source of that toast. Second app covers system also IIRC, whereas first is only for installed apps.

Let's find out what is the source and next steps would follow - if it is an app causing it uninstall it - OP found the culprit app and uninstalled