[gdoc Error requesting data: Failed to connect to

Hi,
well your shortcode is almost written correct. You forgot to add HTML link.
From: Quick start

If using a Google Spreadsheet, the spreadsheet must be shared using either the “Public on the web” or “Anyone with the link” options.
<…>
After saving the appropriate Sharing setting, copy the URL you use to view the Google Spreadsheet from your browser’s address bar into the shortcode.

So the correct looks like this:
[gdoc key=”https://docs.google.com/spreadsheets/d/1DmdR0KlN3N3byIqlCvMguYO90snmztsUUlf2SIyOn-Y/pubhtml”%5D

It works fine for me.

Connection error could be caused by lots of reasons:
(IP which is IPv6 type, belongs to Google servers)
• Google servers were unreachable, what is almost impossible.
• Something in your website interfaces and block this specific connection, sounds weird…
• Your hosting company or your server setup either blocks or doesn’t support IPv6 protocol, possible but kinda weird why at all it’s calling IPv6.
• There is bad configuration and server could not establish any outbound connections.

So these examples are possible and no one can say what exact happened. Who know might Google were updating it’s services. 🙂
(However if it repeats is something on your end)