Google introduced this feature with Android 5.1 but for some reason due to a bug, it disappeared in Android 6.0 and made a return with Android 6.0.1, but like we said reports from Android users who have updated to Android 6.0.1 claim that the feature has for some reason vanished on them once again.
At the moment, it does not appear to be device specific meaning that it could just as easily affect one brand of handset versus another. However given that only Nexus handsets have been updated, it has affected various Nexus owners ranging from the latest Nexus 6P and 5X devices to older Nexus handsets like the Nexus 5 & 6.
In any case, it is obvious this is a bug that needs to be addressed but until Google actually patches it, users who do rely on the feature will need to come up with a workaround. Thankfully it is still Sunday so if you have to wake up early for work or school tomorrow, this should probably be worth looking into.