Bug 406508

SUMMARY
Dolphin only shows metadata of files stored on indexed locations
and if "Also index file content" option is checked in system settings > search > file search kcm.
After you modify "Also index file content" option, the index of the files already indexed before your modification is not updated.
This means that if "Also index file content" was unchecked and you just checked it, Dolphin will continue to not show metadata of the files that were already stored on indexed locations before you check such option.

STEPS TO REPRODUCE
1. uncheck "Also index file content" option in system settings > search > "file search" kcm. 
2. create a new folder in any already indexed location
3. copy videos or pictures to the just created folder
4. set Dolphin to detailed view mode
5. right click on any column, hover over "Image", check both "Width" and "Height"
(notice that both "Width" and "Height" columns are empty)
6. check "Also index file content" option in system settings > search > "file search" kcm
7. create a new folder in the same already indexed location
8. copy other videos or pictures to the just created folder
9. right click on any column, hover over "Image", check both "Width" and "Height"


OBSERVED RESULT
As expected, Dolphin shows the metadata of the files stored in the folder created in the step 7, but it still does not show the same metadata of the files stored in the folder created in the step 2.

EXPECTED RESULT
file indexing should be updated after you check "Also index file content" option
in the step 6, so Dolphin also can show the metadata of the files stored in the folder created in the step 2.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.15.4
KDE Frameworks Version: 5.57.0
Qt Version: 5.12.2