I've found smart lock doesn't work reliably at all, and that's on different devices. It'll allow smart unlock when kilometers from home, yet won't allow it when sitting in the living room. Probably should rename it to "hit and miss" unlock.
Just found out it was an update to the google play services app that broke it. Up to google to fix it but apparently you can disable updates in google play then turn off updates in the play store for all apps if you want to go that route.