Photos 404 errors when subfolder is set

Hi,

When I set up a subfolder for user’s photos upload, the photos return a 404 error.
When it’s not set up everything is displaying fine.

I think there is another problem linked to this one : we are dividing medias by years and month on our install and it always creates the 2016 / 10 folders in the subfolder.

Thank you for your help
Best Regards