The problem I have is that media (images, pdf, etc) uploaded to a the main site (id=1) in a multisite are accessible from subsites domains. Subsites are mapped to different domains.
I upload an image to the main site media library and it can be accessed at both these addresses:
www.site1.com/wp-content/uploads/imageA.jpg www.site2.com/wp-content/uploads/imageA.jpg -> this should not exist
even though it's not visible in site2 media library.
"Use Year month Folders" for uploads is set to 0 (inactive) in the main site settings and 1(active) in subsites settings so the file structure for media content is:
www.site1.com/wp-content/uploads/imageA.jpg for main site www.site2.com/wp-content/uploads/sites/2/2018/07/imageB.jpg for site 2
Edit: this behaviour appears to be present in all the multisites I've tested.