It’s actually a little different than that. If you take the ZHA coordinator off line (not all individual devices) and wait long enough for all the battery powered devices to wake up and realize that the network is out, then everybody will find their new neighbors when the controller comes back. This is an important feature in zigbee, and used in the sensor nets that deploy thousands of devices. It why unplugging the hub forces a network heal for ZHA.
But there has to be a decision point forced.
ZLL doesn’t require a coordinator, though, so you can’t force the rebuild the same way.
The range and repeater FAQ has some examples.
On the Osram bulbs, I’m sorry to hear it, but I believe it. Although since they have done a couple of different firmware updates, and they do use different profiles in the EU and in the US, there’s always been some question as to whether every lot has the same behavior or not. I’d really like to hear their engineers verify The current intended architecture.