Not Enough Space

I have a 8 TB my CLoud Mirror running RAID 1. The dashboard said I have 3.4TB free, smartware says 3.1TB and from SSH, I have this:

Filesystem Size Used Available Use% Mounted on
%root% 54.2M 30.5M 21.0M 59% /
/dev/ram0 54.2M 30.5M 21.0M 59% /
mdev 248.4M 32.0K 248.4M 0% /dev
ubi0:config 12.2M 140.0K 11.4M 1% /usr/local/config
/dev/loop0 91.8M 91.8M 0 100% /usr/local/modules
/dev/sda4 944.9M 40.0M 894.8M 4% /mnt/HD_a4
/dev/sdb4 944.9M 17.3M 917.6M 2% /mnt/HD_b4
/dev/md1 3.6T 515.4G 3.1T 14% /mnt/HD/HD_a2

3.1TB free. I have a folder inside it with 17GB file. I tried copying data manually into it, but I kept on getting a not enough disk space. I created case in the support and they told me to factory reset the device, which I did, btu the issue was not solved.  What do I need to do?

You’re not using WD 2go, by chance, are you?

No, cloud access is disabled as well; we never allow any of the files to go out of the office.