Doorbell chime suddenly stopped working

I've had my Simplisafe video doorbell for a couple of years, has always worked fine.  My chime is a standard analog variety, has always worked without the Chime Connector.

All of a sudden, the chime has stopped working. In all other respects, the doorbell seems to be OK. Tomorrow I will pull off the doorbell and reboot it, also will disconnect and touch the wires together to confirm that the chime is working at all.  Anything I should be looking for?