I tried http://www.thesayansblog.net/2017/11/re-enable-nfc-smart-lock.html but it didn't work for me.

I have found another way to re-enable the NFC Smart Lock feature on Android, though it still requires root and manually editing a preferences file.
Details on pastebin: https://pastebin.com/2RSZzERg

Heads up, with this workaround we might re-enable NFC Smart Lock: http://www.thesayansblog.net/2017/11/re-enable-nfc-smart-lock.html

AFAIK you need to downgrade Play Services, enable NFC Smart Unlock and then update again. I haven't tried it myself yet, though.

This needs more visibility. If we can get enough users to star this issue, maybe Google will review it and reconsider bringing back NFC to Smart Unlock.

Now there's an official statement from Google. They're deprecating NFC unlock because of "low usage" and have already removed all references to it from their online manuals.

This and the lack of communication might very well signal the end of the NFC ring. Not even the much-vaunted payment-enabled model will make up for the loss of this feature.

Came here to comment about this issue. Apparently, even if you still have the NFC Smart Lock feature enabled and working so far, you will lose it when you factory reset or otherwise log out of your Google account on your Android device. Here is a reddit thread with a good writeup on the subject: https://www.reddit.com/r/Android/comments/72tj6u/psa_google_have_quietly_removed_nfc_smart_unlock/

Can confirm 2016 rings work with Virdi AC2100:
http://www.virdi.eu/produkty/1,terminale_biometryczne_+_rfid/2,virdi_ac-2100.html

It might have something to do with Android Pay, or some other related app that has support to make payments via NFC. I've heard these need the device to have the lockscreen on for safety.

You'd have to convince the staff to register your ring as a valid tag, if they are compatible. Most of them are, the hard part is the convincing...

No, the 4-hour timeout is a different behaviour (and intended, it seems). That is, the Smart Lock feature disabling itself after 4 hours of inactivity. I think it takes longer than that.

On the other hand, the bug seems to cause the NFC radio to stop polling for tags after locking. So even though Smart Lock is enabled, it can't read them.

I've had the bug multiple times in less than an hour so it is definitely not the same as the stated timeout.

In any case, the Xposed module does nothing about the timeout. I still have to draw the pattern once every morning. But not during the day after that. Sometimes, it takes a bit longer to read the ring and the screen turns off before unlocking, but then it usually reads right away after turning on again, so it works for me. YMMV.

If by "disrupt normal battery features" you mean consuming more battery, that is in fact is one of the reasons I removed the option to enable NFC on when the screen is off. As it is now, the module can only enable NFC when the screen turns on, which is what the Smart Lock feature should be doing anyway.