Ah, good lock almost never works on betas. Since it's a separate app, the app itself needs to be updated to support the new operating system. That usually happens after the full release comes out.
For the app not working, you might have found a bug. If it's one from the play store then it's kinda expected but still good to report. If it's a system app, definitely report that.
And for going back, you will have to wipe your device and use a computer to downgrade the phone via smart switch