Update Index Items not working

Sometimes, when I add/change/delete a file to an indexed folder in Finder it updates without me doing anything.

Sometimes, I have to select the DT3 Group and hit Update Indexed Items and it works.

And then sometimes (like now), it’s not working at all.

(I did empty the trash in DT3. I read that could be an issue, but it didn’t help me).

Are you indexing in Dropbox, iCloud, or some other cloud-synced location?
If so, manually using File > Update Indexed Items may be necessary as noted in the Help > Documentation > In & Out > Importing & Indexing > Indexing and the filesystem