What is the "code" after the app package name in /data/app/?
That's a random string appended to apps installation path in order to force developers don't hard-code paths in apps, instead use proper APIs.

Quoted from Android 8.0 Behavior Changes:


  You can no longer assume that APKs reside in directories whose names end in -1 or -2. Apps should use sourceDir to get the directory, and not rely on the directory format directly.