Huh, odd. Can you check to see what your android:launchMode is set to in AndroidManifest.xml? If you don't have access to it you can run "aapt l -a name.apk" where "name.apk" is the file name of your Android apk. Also, check to see if your phone has developer mode enabled and if "Don't keep activities" is checked under the "Apps" section of "Developer Options". My educated guess is that the latter is what is happening.
I checked the AndroidManifest.xml and its set to "singleTop". Developer Options have it unchecked. We're now doubting ourselves if it ever worked properly as there are some mixed opinions between the devs. To be honest its not something we ever actively tested. By following this article we just managed to find a solution to force the launch mode: android - Phonegap single instance - Stack Overflow
Changing the settings in config.xml as per the instructions here didn't work Config.xml - Apache Cordova