I had some luck on this one.
I initially onboarded my nanoleafs into home assistant using Apple TV as preferred thread router & my ios device, this resulted in the unavaliable issue dropping in and out etc.
I have google nest wifi pros as my home mesh network, I was also able to find a spare android device, so I decided to swap the google nest wifi pros as the preferred network then re onboard the nanoleafs using android.
Since doing this i have not had a single drop out. not sure if that will help anyone but it worked for me so thought I’d share.
It’s an unfortunate solution as means I can’t use my primary phone to onboard new matter devices. but it works 