"Mount error 13" on CIFS connection w/o Domain Admin

Question

Scenario

I have following clients in my network:

• Quartz I2S scanner with embedded Linux firmware
• Windows client (not domain-joined) for comparison

These will be trying to access a network share on domain-joined Windows Server 2016 using a domain account DOMAIN\test being a member of Scanners security group upon which all CIFS/FS privileges are based.

Problem

Scanner fails to connect to the network share.

The only debug I can get from the OS is this error line thrown on the console on each instance I try to test the share via GUI:

mount error(13): Permission denied

I cannot however check or influence the command line embedded in the software, that is used to mount the share.

But... (weird part)

I can make the same connection (share/user/password) from Windows client and it works properly. This means to me that all the privileges (CIFS and FS) are correct and the credentials are OK.

Now, along further tests, I've discovered this:

• when I add the DOMAIN\test user to the Domain Admins group, scanner gets connected to share and everything works properly,
• when I remove the user from Domain Admins group, it keeps working properly until restart.

What might be causing this?

Update 1

I've managed to log onto the console and attempt to mount the share manually. All I get beside the error line above is the:

CIFS VFS: cifs_read_super: get root inode failed

That's all. No other error codes before that line.