New - RBR850 / RBS850 Firmware Version 4.6.14.3 Released

I use my RBR850 in access point mode, not router mode. I use a different DHCP server (ie not my Orbi) to assign IP addresses to all devices on my network, including the Orbi's, and I have those IP addresses set up in a local DNS server (also not my Orbi). With this setup, I can go to https://ap1.example.com (not the real domain name, but you get the idea) and get the RBR850 login prompt, after which I can access the web interface for the router.

Just updated 3 RBS850s and 1 RBR850 to V4.6.14.3_2.3.12. Post upgrade, accessing the web interface on the RBR850 generates an HTTP error 500 (Internal Server Error). I can access the web interface by using the ip address directly, ie https://10.10.10.36 (also not the real ip address, but you know....). On the RBSs I can access their web interface just fine via https://ap2.example.com. Once I have accessed the web interface, everything seems to work fine, satellites are synced, WIFI works, etc.

I did a factory reset on the RBR850, and restored settings from backup. Same result. I did another factory reset, and manually configured all settings without doing a restore. Same result. I've tried multiple browsers on multiple computers, including clearing browser caches. Same result: HTTP Error 500 Internal Server Error.

Anyone have ideas how to troubleshoot and/or resolve this?