MBP 15" mid 2012 running Sierra 10.12.2, 16Mb RAM, Studio One 3.3.3-latest build. -- attached to both a new Faderport 8 and older single Faderport.
Tried to drag & drop a new instrument onto track... but couldn't get anything out of it. Check and found that my Keystation 49e was not connected. Happens sometimes. Went into Preferences and it was in fact Not Connected. Tried to re-connect... it's not on the list and even when I manually add it, it will not connect. It is getting power from the USB cable, so I know it is connected. It appears on the MIDI list in the Midi/Audio utility, but I'm not sure it's sending data. Not sure how to test for that.
Worked in the last week or so. Not sure what's going on. Any suggestions or trouble shooting info welcome.