I am using Premiere Pro 15.2.0 on macOS 10.13.1 and scene edit detection works fine for me.
Trying following might resolve the issue -
1. Reboot your system and try again
2. Try different clips with different format and see if anyone of them works.
or 3. Try Reset preferences, follow this step:
Press Alt (Windows) or Option (Mac OS) while launching Premiere Pro. You can release the Alt key or Option key when the splash screen appears.
To reset preferences and plug-in cache at the same time, hold down Shift-Alt (Windows) or Shift-Option (Mac OS) while the application is starting. Release the Shift-Alt keys or Shift-Option keys when the splash screen appears.
Vishu Aggarwal Adobe Certified Instructor, Professional and Expert
Fresh install of Premiere 15.2.0 on a fresh install of OSX 11.3.1 on 8-core intel i9 with 64GB and mine didn't. I versioned back to 14.5 and it worked like a charm. Premiere was also super sluggish, lots of beachballing, and just overall not pleasant to work with.