Recording level 'greyed out'

So, Ive been reading a gazillion posts on this subject and all the well-meaning replies suggest the usual basic things to check:

• Mac sound inputs
• Interface's own input controls
• Track volume slider
• Etc etc

I'm having no success with either of these suggestions.

I'm recording in Garageband on a MacBook Pro and it was working fine then suddenly, seemingly unprovoked, it stopped accepting input from my Focurite Scarlet 2i2. I'm what I would call an avid user of Garageband, but I simply cannot comprehend why it suddenly stopped working.

The Mac itself recognizes the input, there is plenty of gain coming from the interface to the Mac, but for some reason Garageband won't accept it. Is this a software update glitch, Apple? The hardware seems to work...

Any new suggestions will be greatly appreciated, thank you.