Logic Pro X, Audio interface problem

Hello Fam,

I record my guitar into Logic Pro X using a Scarlett 2i2 audio interface. A few days back, out of the blue (after changing to a bass really, but shouldn't have made a difference), the sound wasn't coming through the headphones when I played the guitar. Logic Pro was picking up a signal, the Scarlett was picking up a signal, but there was no coming through. But: if I record something, I can't hear it while recording but the playback sounds OK.

Any thoughts?

Thanks

p.s. is it me, or the Logic Pro X - Scarlett 2i2 can be super buggy?