All IKEA temp sensors became unavailable in HAOS at the same time

What Happened
I have 6 IKEA TIMMERFLOTTE sensors dotted around my home. I set them up using the Apple Home app, and then added them to my HAOS instance using the "Turn On Pairing Mode" function in Home.
I was them able to create some graphs in HAOS that displayed the historical temperature and humidity.
This worked fine for a couple of weeks, then one day all 6 sensors became unavailable at the same time, and have remained unavailable since.
The Apple Home app continues to report temp/humidity from the 6 sensors.

My Setup

  • HAOS VirtualBox image is running in a VirtualBox VM, VirtualBox is running on an MacMini. The Mac Mini is connected via Wi-Fi (it's located somewhere where I can't run ethernet).
  • My HAOS instance doesn't have a prefered Thread Network, but it reports both Apple TVs as border routers.
  • A UniFi Dream Machine Pro does all the routing and IPV4 DHCP, using a PiHole instance to provide DNS for the whole network.
  • All TIMMERFLOTTE sensors are running firmware 1.0.21, which is currently the latest vresion.

What I've tried

  • I restarted all 6 sensors (remove batteries).
  • I factory reset one sensor, and unsuccessfully attempted to add it directly to my HAOS instance using the HAOS iOS app.
  • I factory reset the same sensor, successfully added it via the Apple Home app, but I can not then pair it with HAOS.
  • Verified that IPV6 is enabled in my HAOS network settings.

HAOS was hapily recored data from the 6 sesnors until they all became unavailble at the same time. I'm new to HAOS, and IPV6, so I need some pointers on were to start investigating the issues.

All suggestions welcome.