After several more rounds of of testing, including repeating everything mentioned above on 3/28, plus the following:
- Unenrolled everything from the network, performed a factory reset on the Aeotec z-stick
- Performed factory reset on the lock
- Repeated everything again
Eventually, given the age of the lock (manufactured in 2008), I started wondering if the firmware on the lock was just too old, or if there was something wrong with the lock - it has acted strangely in the past to the point where I had to use the physical key to unlock the door a few times, but hasn’t acted up for months.
As a last resort, I purchased a new FE599 to see if the issue was with the old lock or something else with my Aeotec z-stick or on my system. The new lock enrolled faster than the old lock, I was able to change the group association without any issues (still no groups in the drop-down for the old lock), the lock responds instantly to lock/unlock requests from HA, and HA updates instantly to any activity with the lock.