I removed a light fixture to find this wiring in box. 4 sets of 12/2 wires coming into ceiling box for light fixture. One is power, one goes to switch for light fixture. Other two go to an exhaust vent over stove. There is a light switch and fan switch on vent. When looking closer at wiring, I noticed that there was a ground wire with a green wire nut that was 'on' the wire. I.E. someone put a hole in end of wire nut, and ran wire through wire nut. I don't believe this ground wire was attached to any other wires, seemed loose in box when I pulled on it. Ground wire comes from either vent light or vent fan. Additionally, light fixture white wire is wired together with black wires from power source and vent light and fan. Then when checking switch, there is only the white wire attached, black wire has been twisted around the white wire. After taking light fixture down, I lost power to the vent fan and light. Never seen anything like this before.
The green wire nut with the hole in the tip is normal. Green wire nuts are the same size as red, except they have a hole in the tip. That's why they're color coded green, to tell you that. And they're for exactly that use.
All ground wires should be connected to each other, and also to any appliances or devices and also the metal box if metal.
The switch is what's called a switch loop. It's an older style one with /2 cable (black, white) and no red. In a switch loop, the white wire should be used as always-hot and tied in with the blacks. The white wire is chosen to be always-hot so it's more obvious when you're checking it with a voltage tester. It should also be marked with tape to indicate the white wire is a hot, this step is often overlooked.
It sounds like the other cables in the box carry onward power to other devices, e.g. the hood.
It would help to have photos of what is going on in those boxes.