CENTOS 7 can't edit files on a shared Windows folder

I have the following very peculiar problem:

We have a Windows server 2012 R2 server with some shares on it. I'm trying to get them to share via SMB3 at the very minimum. No problem with our Windows or Ubuntu clients. However the CentOS 7 clients are being a nuisance.

I have forced the Windows Server 2012 R2 to only use SMB2 and 3 with:

Set-SmbServerConfiguration -EnableSMB1Protocol $false

And I'm trying to get the clients to only use SMB3 by adding the line: Client Max Protocol = SMB3 in /etc/samba/smb.conf under [global]

I can access the shares now. Users can create, change and remove folders. They can also create and remove files. But they can't change them afterwards and neither can any other users with access to this share.

Could not save the file "smb://winbox/share" Unexpected error: Invalid argument

Using: Get-SmbSession | Select-Object -Property * I can see they connect to the server using SMB3.

Does anyone have an idea how to fix this? This could probably be solved if I forced our users to create an FStab file and use CIFS with vers=3.0 but I'd prefer it if they could just use the File Manager for their filesharing. (Easier and not all of our CentOS users are Techs)

Ps. I've also tried it with a different Windows Server 2012 R2. Same problem.

Thanks in advance.