Buster: Dolphin Ctrl+F: baloosearch on some dirs, filenamesearch on others

[local10 <local10@tutanota.com>]

Hi,

For some reason KDE Dolphin invokes (after pressing Ctrl+F) baloosearch on some directories and filenamesearch on others. Baloosearch does not work for me (that is, shows 0 folders, 0 files even when there are files matching the search criteria) while filenamesearch works fine. Why does Dolphin invoke baloosearch on some directories and how do I disable baloosearch and make filenamesearch work on all directories?

In KDE System settings > Search > File Search I have:
  [X] Enable File Search (checked)
  [ ] Also index file content (unchecked)

Any ideas? Thanks