After a lot of tinkering around with this, I've come to the astonishing and earth shattering conclusion that the Raildar map, well... sometimes works, and sometimes doesn't!!
Have attempted dozens of times using 4 different browsers, both with and without deleting cookies and browser data using CCleaner Pro to find a cause.
There is absolutely no pattern, for example a failed attempt using Chrome will be immediately followed by a successful one with Firefox etc etc, but as I say there's no pattern.
By the way, a purely non scientific observation I made is that the Arc browser with I downloaded yesterday seems to have a far higher hit rate than all the other browsers.
One of the causes of the error you quoted is described as:
Why is this error appearing in the first place? In the past, the "This Page Can't Load Google Maps Correctly" error didn’t constitute an issue because Google ran other procedures.
Later, Google changed their procedures and they are now requiring a Google API key and a Google Cloud Platform billing account to use Google Maps. This change was applied on June 11, 2018. Since then, the "This Page Can't Load Google Maps Correctly" error seems to be encountered more and more often by those who are not aware of the change.
Thus, the main cause behind this error is the API key requirement. Because Google Maps is embedded on important websites that get a lot of monthly views (over 100,000), the company thought of a method to make money by adding a fee for high-volume users.
The API is still free for smaller websites that don’t get a lot of hits, but bigger websites are now charged for using the API.
So it's possible that the raildar website is now receiving significantly more hits that the its API licence will allow and it's almost always fully subscribed?
So for you to get in you need to be the first user to try after someone else has left the site.