The recently published version 2.0 of Watch my Bluetooth Devices was locked by Google shortly after publishing.
Meanwhile Watch my Bluetooth Devices is available again in the Google Play Store but unfortunately it cannot be installed as an update for older versions.
This means you have to uninstall an older version of Watch my Bluetooth Devices before installing the current version available in the Play Store. Otherwise there is a chance that two installations of the app are running in parallel which leads necessarily to a faulty behavior.

OK