I suspect since you’ve been fairly thorough in your setup and analysis, you may have a defective lock or chipset in the non working lock. If it’s saying that beeper is unknown it isn’t responding correctly.
If you haven’t already tried it, try to replace the battery. If not you may need to request Schlage for a replacement lock. If you’re considering new locks, check out Yale. It has a few more handy features/flexibility and the zwave module is replaceable. You can even get their newer zwave plus locks which have a better battery life.