Record enabled, monitor on but no sound

Exactly that. I have no idea why, or what setting I’ve unwittingly changed recently, but today I’m having this problem.

I have a track set to record a mic. Mono input, stereo output. On the mono input channel I can see the green activity waveform, and recording works, but I hear nothing in my headphones while recording. I have the monitor button enabled, and it has worked before…there is no output signal - what am I missing?

ASIO crashed, restarted, all good. Sorryyyy!