Schlage in general has been pretty notorious for Z-wave compatibility issues in the past across multiple product gens, some tickets may or may not be related.
This thread is relevant to this question.
Alarm.com no longer lists the FE599NX on their supported devices list. The FE599NX is not compatible with the latest Z-wave radio versions used in Alarm.com modules and panels. It is only compatible with the older 300 series radios. Your panel has a newer 500-series radio.
Additionally, other Schlage models BE468 and BE469 are only supported if they were manufactured since December 2019.
You can try updating firmware to see if there is any improvement in functionality. Your panel is running a handful of versions behind the latest, and there have been some Z-wave changes. However, I don’t believe the issues with the FE599NX will be resolved.