The GE bulbs dropping out is likely a GE specific problem. They have a firmware issue where occasionally they lose touch with the network. It’s very annoying. And it’s the reason why the GE bulbs are not on the official “works with smartthings” list. When I started out I had eight of these bulbs and two or three of them would do this once or twice a month. Different bulbs each time. But my bulbs of other brands never had this issue. Eventually, I got a Hue bridge and replaced all of the GE links with the $15 Hue whites. No more problems.
There’s an FAQ just for the GE bulbs.
Now the good news. 
As far as healing the zigbee mesh, just do the power off method first. The whole reason that method was designed into the zigbee protocol was so that you wouldn’t have to fiddle with each individual device. Zigbee is a “self healing” topology: you supply the power, the network builds itself. If the problem is you’re seeing are being caused by An inefficient network, the simple power off method will fix that. It can take a while for each individual device on the network to complete rebuilding its own neighbor tables after the hub comes back on power, so you may not see results until the next day. But at least it’s easy to do!