AP7921 PDU Boot Issue w/ Global Outlet Groups

[holtzp_apc]

I've got some AP7921 (not B) PDUs running rpdu and aos firmware 3.9.2 that don't boot properly when global outlet groups are enabled and plugged into my production network. Their display stays at "88" for several minutes before I'm able to access the web GUI and all outlets default to Off despite being configured for Immediate On. The global groups do otherwise work, however. I only discovered this issue after a PDU recently lost power, so I don't know when it started or if it was precipitated by a network change or PDU firmware update.

The PDUs boot correctly with global groups enabled if they're plugged into an isolated LAN by themselves. They also boot correctly with global groups disabled and plugged into my production network. I saw https://www.apc.com/us/en/faqs/FA231707/ but don't have any AP8XXX devices on the network and each pair of AP7921 PDUs have a unique multicast address.

Are there any other known issues that could cause this with firmware 3.9.2, or any troubleshooting suggestions?

Thanks!

Paul