I’m posting this in case it helps someone else. I am no longer having problems. I used to have problems where my Wiz lights would routinely become unavailable. They would be unavailable in Home Assistant as well as within the Wiz app itself. I have found the root cause in my case and posting it here in case anyone searches in the future for a solution.
My WiFi infrastructure at the house is all Ubiquiti equipment with multiple access points / hotspots around the house.
Initially I had two WiFi SSIDs, MyNetwork-5GHz and MyNetwork. The SSID for MyNetwork was tied only to the 2.4GHz channel and was used for mostly IoT devices including the Wiz lights. Within my Ubiquiti configuration both networks would run on all hotspots. Devices could roam from hotspot to hotspot as signals changed.
WIz lights hate roaming. This was the cause of the lights becoming unavailable.
My solution was as follows.
Leave the non IoT network, MyNetwork-5GHz running on all hotspots. Devices such as iPhones etc are happy to jump from hotspot to hotspot.
Create a new SSID using only 2.4GHz dedicated to each hotspot. I deleted the old WiFi SSID MyNetwork (the 2.4 GHz one). For the naming scheme I just put two letters in the SSID designating the hotspot. Examples: FP Front Portch, RP Rear Porch, MB Master Bedroom, MR Media Room etc.
My SSIDs now look like this
MyNetwork-5GHz (all access points)
MyNetwork FP (2.4GHz only, only runs on front porch access point)
MyNetwork RP (2.4GHz only, only runs on rear porch access point)
MyNetwork MB (2.4GHz only, only runs on master bedroom access point)
MyNetwork MR (2.4GHz only, only runs on media room access point)
Within the Ubiquiti Network setup using the access point groups I tie for example MyNetwork FP to only the Front Porch access point. and so on.
Reconfigure each Wiz light to use the closest / best access point / hotspot. For example the Wiz lights on the rear porch are now configured to use the WiFi SSID MyNetwork RP
Since doing this I have not had a single Wiz bulb become unavailable. I have also noticed improved WiFi connection “score” (a Ubiquiti term) for some of the other IoT devices I have.
I am are that this is very Ubiquiti specific but more than likely the concept would work for any WiFi hardware vendor when you have multiple access points.