I’m pretty sure the bulbs do not reconnect when they go offline because they are actually locked up/crashed. I have watched a continuous ping to them and noticed when they get within a few minutes of crashing, they start dropping packets about 50% of the time until they stop responding all together. One of my bulbs always did it first, then the others usually followed behind either a few minutes later or hours later. All gen3.
I moved mine to their own ssid on their own AP which improved the crashing from a couple of hours up to around 24 hours. Then I moved them over to their own vlan which was entirely separated form my normal lan. After this, they never disconnected again for at least 2 days. But now they responded a lot slower through the app because it was forced to go through the internet for any changes. I am now trying to return these. Too expensive for a beta product.
In my testing I have determined the cause is not wireless interference, not my networking equipment (unifi ap and gateway), and not the android app. It is something the bulbs can’t handle on my normal network, something they should be ignoring but are not and it is causing them to eventually crash. Happens more often when I am actively using my main PC (gaming, youtube, etc.). But your guess is as good as mine as to what the actual cause is. I read another user had determined it was his raspberry pi that was causing it and once he disconnected it from his network the bulbs stopped crashing. Again, not acceptable for a wifi device such as this to be so fickle.