Spotlight not indexing Applications on High Sierra

Help!

Spotlight is probably my favourite way of launching apps on macOS. Annoyingly, a couple of weeks ago it seemed to "forget" my applications.

I have rummaged through the forums and performed the same trickery as recommended in most places:

• Stop the indexing process with mdutil
• Delete the index
• Start the indexing process

and also

• Go into Settings > Spotlight
• Either:
  • Drag the drive in to the Exclude list, then remove it
  • Or un-check Applications, then re-check it
• Then wait 5 minutes and everything appears again in a search.

Except I've had no luck with either approach.

Is there an absolutely foolproof way of getting Spotlight to work properly again? I'm on High Sierra (10.13.3).

Thanks.