Google has been talking about Instant Apps for a few years now, but it only turned developers loose on the tools around the middle of last year. With Instant Apps gaining popularity, users have started to notice some strange behavior. In Android 8.0, Instant Apps appear to break the ability of the PackageManager to return a list of installed apps.
According to the Issue Tracker thread, Instant Apps interfere with the getInstalledPackages and getInstalledApplications commands. Apps use these to find a list of other apps on your phone. You might need that in apps that manage notifications, storage cleaners, or Google's own Files Go app that tells you when apps haven't been used in a while. After installing an Instant App, these commands just return empty lists.
You can see a demo of the issue in the video above. Googlers in the thread have confirmed the issue, saying it's reproducible in Android 8.0. It seems like most (possibly all) Android 8.0 devices are affected. However, Android 8.1 doesn't seem to be affected. Google is looking into a fix for affected devices.
- Issue Tracker