When uninstalling and older version of KeyShot while a newer version is installed it can remove the Preview from BIP files. Below are some options to fix the issue. 

Two options for fixing missing Thumbnails
You can re-run the full KeyShot installer and install over your current KeyShot Installation. No need to uninstall current KeyShot installation.
You can register the Preview handler found in the KeyShot bin folder. Open Command Prompt in administrator mode.
Type in 
cd C:\Programs Files\KeyShot 9\bin\KeyShot-ih.dll

You may need to adjust the path to point to your installation directory.

Note: More common to happen with updated installers being used.