MRUK stopped working on Android build in v77

We've been developing MR features into our app for the past 6 months and recently started testing a release candidate for Horizon Managed Services (HMS) managed headsets (enrolled with ArborXR). We ran into an issue with the Immersive Debugger causing exceptions on headsets set up using HMS/Arbor when using SDK v74. We updated to v77 which fixed the Immersive Debugger issue, but then the MR features stopped working also on headsets running "personal" accounts.

It seems like the MRUK is not creating the rooms in the scene, and thus our app doesn't initialise our custom room set up. I've seen posts about needing to have the app registered in the Developers Hub, which we had in the past but deleted. We've created new apps in the developer hub and registered them in the Unity Tools>Platform settings for the Meta SDK and still nothing.

We get a log from MRUK Shared saying "Unable to bind OpenXR entry", which I suspect is the issue causing the MRUK to not work. Everything works fine in the Simulator, I've tried also updating the version of the OpenXR plugin, everything I could find online, and still nothing.

We are using Unity 6 (6000.0.42f1), Meta SDK v77 with OpenXR integration.