“Update index” command not updating the indexed folder

I have 1 DT3 db where I indexed a folder.
I added 2 folders within this (indexed) folder.
The new subfolder are not visible in DT3.
So I launch a update indexed elements
and the subfolders are not appearting in the dt3 database (under the main indexed folder).
I created a new db DT3 and indexed the same folder and then the new subfolders appear.