New Google maps loading error: not-loading-api-from-google-maps-error

My app uses Google Maps API, and has worked well so far. Yet, when trying to update my Android app, I get the awful white page with the message:

Oops! Something went wrong.

My web app works fine, it is just the Android one (same HTML, same JS) which has problems.

I then went to the javascript console in Android Studio, and it says:

[INFO:CONSOLE(139)] "Google Maps JavaScript API error: NotLoadingAPIFromGoogleMapsError

with the link

 https://developers.google.com/maps/documentation/javascript/error-messages#not-loading-api-from-google-maps-error

I went to that page, and it says:

 NotLoadingAPIFromGoogleMapsError: The script element that loads
 the Maps JavaScript API is not being included correctly on your page.
 In order for the API to work correctly, it must be loaded directly from
 https://maps.googleapis.com.

Yet, I load the API with the lines:

 <script src="https://www.google.com/jsapi"></script>
 <script src="https://maps.googleapis.com/maps/api/js?key=...."></script>

which is of course the Google server.

Again: My web app works fine, it is just the Android one (same HTML, same JS) which has problems.

To make things even more strange, I have another Android app that uses Google maps as above, without problems.

What is going on?