Smart lock not working anymore with trusted places
It might have something to do with this issue: Issue #79735: Smart lock feature (trusted face/device) not working when screen is turned off using software screen off command (DevicePolicyManager.lockNow)

In short: Smart lock breaks when any app uses "soft power off", i.e. your screen is turned off by an app or in any way except the hardware button or a normal timeout.

Note that when this is the case the small pulsating circle around the lock symbol (at the bottom of the lock screen) is missing, since all smart lock variants are disabled (e.g. trusted faces also doesn't work anymore).