Shield won't see my drive

[TerFar]

My Shield sees my 128GB USB 3.1 pen key without a problem and I can play UHD movies from it perfectly. But in order to get more storage, I'm trying to use a 500GB SSD. It's mounted in a 2.5" Inateck USB3 SSD enclosure and connected using a USB3 to USB3 cable.
This works absolutely fine on my Windows PC and on my Acer Chromebook. But the Shield sees absolutely nothing, as though it isn't connected.
Is there some hidden limitation with Shield or have I some strange problem?

 

[GSDer]

Sounds like the latter. I have a regular Seagate HDD connected to mine and it seems to work fine: it shows up in Storage; I'm able to view files on it; eject it as appropriate; I use VLC to find and play movies.