Thomas Wel… I haven't changed anything, just selected the folders inside instead of the upper folder, and it started working as I expected. The problem is easy reproducible for me, so I think that is the solution for the time being :-)
The folders or pictures do not have special characters, we store them in Sharepoint and Creative Cloud and other kinds of storages so we are aware of special characters and avoid them in file names. But since I started selecting the inside folders, it started working.
The main folders do not have any special characters, unless accents are considered special, such as í or ó.