TL;DR: Something to try if you have issues with ZHA initialization of existing network: disable the ZHA integration; reboot with the integration disabled; let HAOS run for a bit and then re-enable it. No idea why.
I'm using a "SONOFF Dongle Plus MG24" as the zigbee network controller. It has been working fine until yesterday when ZHA got in a funky mode and seemed to hang indefinitely during initialization. I tried rebooting. Rebooting to safe mode. Rebooting again. No success. ZHA would just hang for 30 mins (my tolerance window) or completely give up with a very generic error message and no devices connecting. I was about to update the device firmware when I thought I better grab any information from ZHA I might need for recovery/migration after the firmware update. So I went back to HAOS where the ZHA integration had been disabled overnight (~12 hours). When I re-enabled it, devices slowly reconnected and the whole network was back online in 5 mins or so. I'm still not sure what happened but I thought I'd leave this here in case it helps anyone else.
Additional context: HAOS is qemu+libvirt on RPi5. Roughly 20 zigbee devices.