net::ERR_CONNECTION_TIMED_OUT The message in the title appears at the bottom of my screen every minute and goes away after a couple of seconds. It's very distracting when I'm trying to read and I can't for the life of me figure out what is actually timing out! 

I can't remember exactly when it started but it's been at least a few weeks, I've been ignoring it but it's started driving me crazy now.

Google suggests it's a problem with Chrome. But even after making sure it's fully up to date, all tabs closed, force stopped the application, rebooted phone. Still does it! Even when chrome isn't running. So I'm not convinced it's a Chrome issue.

It continues to happen regardless of what app is in the foreground.

My phone has plenty free memory and storage and a good connection (I have a strong 4G signal, also tried on WiFi connection with a fibre line, the message continues regardless) these were things my Google search suggested to check, so I did just to rule it out conclusively.

How can I figure out what is causing this message to appear? I consider myself literate enough to follow complex instructions but I am not intimate with the android OS, so please be detailed with any debugging suggestions.

It conveniently appeared while I was getting a screenshot of my versions for this post.



I should note, for clarity, that I am NOT experiencing any connection issues. It's just this message appears every minute and I want to identify the reason.
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