I love this kind of step-by-step solving post, but it bothers me that the author didn't track down what the JPEG in the Alternate Data Stream (ADS) was for. Something put it there... Might it be a surprise when it ends up not being there later?
Also, it kinda sounds like the UNAS might not be supporting ADS' for some reason? That alone could be a problem later on...
Yes, I certainly wouldn't have just skipped past ADS not working. Since samba and zfs support it, this is weird that Ubiquiti wouldn't. If this isn't just a config problem, I would call it cause to return the device.
Also, it kinda sounds like the UNAS might not be supporting ADS' for some reason? That alone could be a problem later on...