The solution on this post added by lukasrein97 fixes the issue. I have no idea why that app was working on Android for six months without this, but it happened.
The solution is:
cordova plugin add cordova-plugin-whitelist
And in the config.xml file add:
<allow-navigation href="http://*/*" />
<allow-navigation href="https://*/*" />
<allow-navigation href="data:*" />