What did you have it set for: trusted places, trusted devices, on body detection? Is it not working at all or turns off some of the time. Extend unlock only keeps your phone unlocked for up to four hours and will lock after a missed text or phone call (and, I think, missed notification) for privacy & security. If you mean it does not remain unlocked at all and you don't see the "extend unlock" on your lock screen, that's a different issue. If you are using trusted places, Google maps does not know the size of the place, so you either have to extend the parameters or set up a routine to add a wi-fi network. If you are using on-body detection, the phone will lock once it's not on body--such as if you set it on a table. It does not unlock automatically under those circumstances. A phone has to be unlocked before it can stay unlocked.
Also, make sure the setting didn't get turned off after an update, as sometimes happens.
