Hi there, I found that the screenshot shows "Partition Map: Not Supported" so I suggest you go to check if the SSD is formatted ad GUID Partition and MacOS Extended(Journaled) first.
Furthermore, the Apple team only plans the Optical Bay to offer support to a slow optic drive but not an SSD which does wonderfully in data reading/writing and transferring. The Optical Bay cannot run the SSD comprehensively.
Apple might fix this trouble by system firmware updating later but you can utilize an external enclosure to handle the current situation. Hope that works~
