Instructions for macOS
Open a Finder window and go to the following location:
Macintosh HD > Users > Shared
Locate the folder named NI Resources and move it to the trash.
Next, click Go in the Finder menu bar while holding down the option / alt key on the computer keyboard. Choose the Library entry that appears in the drop-down menu.
GoMenuFinderUserLibrary.png
In the user Library folder, navigate to the following location:
Application Support > Native Instruments
Locate the Komplete Kontrol and Maschine 2 folders and move them to the trash.
Next, in the same user Library folder, navigate into the folder named Service Center and move the file named pal.db to the trash.
Empty the system trash and then open Native Access:
Macintosh HD > Applications > Native Access.app
Within Native Access, click the Refresh button and allow it to scan for a moment.
Native_Access_Refresh.png
Open the KOMPLETE KONTROL / MASCHINE 2 software in standalone mode and allow it to rebuild its database.
The thumbnails should now appear in the KOMPLETE KONTROL / MASCHINE 2 software Browser.