SFTP destroying permissions?

Hello

I've setup a few shares for multiple users.

For instance "Documents", both read and write access by 3 users. No issues. Can write and read for aslong as I want.

A 2nd folder called "Writes", both read and write access by 3 users (1 mutual being my own - mathieu) doesn't allow me to write. Sometimes it even bugs the permissions causing it to be (from ls -al) d????????? ??? ??? some numbers Writes/ which also prevents me from even being able to read it. (it just disappears from the SFTP access)

The SFTP access is being handled through an Ubuntu 18.04 vm. 

This is what my fstab looks like:

Tried adding the uids after it bugging, doesn't help. 

I've also noticed that the command "tree" is bugged, while having it installed and working correctly before, error: (IDK if relevant)

As we're speaking it's bugged again, remounted the shares yesterday so roughly 34 hours ago, from writing. (then it worked fine)

Now I'm missing all my folders as user student and mathieu except for Documents and movies.

Using umount -av and mount -av obviously fixes this "issue". Any idea how to fix this?

I assume it's because of SMB? I can't write in /Shared for instance now while the user in the webgui has read and write access. 

Thanks in advance