Outbound VPN Under MacOS

My question actually involves the RBK753S — Orbi WiFi 6 System AX4200, running firmware V3.2.16.6_1.4.4 (this model not shown in the drop-down list). Client machine is running MacOS 10.13.6. Issue is that outbound VPN using built-in MacOS client works fine when connected to the Orbi WiFi router via Wi-Fi only. But when connected to the Orbi WiFi router via Ethernet (whether or not WiFi is turned on), the connection fails. This behavior is repeatable, and has been replicated across other machines, so it's definitely related to the Ethernet connection being active. Is there an Orbi setting that needs to be adjusted in the web admin portal, because I don't see anywhere in the app to change settings? Thanks,  --RK