Buying a new hub probably won’t help. This type of issue (usually called “poltergeists” in the forum) is almost always caused by one of three things: circuit load, an automation, or a cloud glitch.
- most of these switches have an overload feature where sudden surges on the circuit Will cause them to turn themselves off briefly, then turn on again, and repeat if the surges repeat. Hairdryers are a classic for causing this, but so can some older vacuum cleaners, power tools, space heaters, anything which causes a sudden high jump in search on a shared circuit. Evenings are typically the worst because everybody is home and there are lots of devices in use.
Because this is a mechanical issue, there won’t be anything in the system logs or notifications to show it happening. 
It’s usually pretty easy to find with detective work, though. I have everyone keep everything turned off except essential lights and appliances like refrigerators. Then start turning on the things that normally get used at night one at a time. Then adding multiples, starting with the most likely culprits. Once you find it, you can probably make the problem happen every time.
The fix is either behavioral: don’t use everything all at once or electrical, bring in an electrician to evaluate the current situation and if necessary add an additional circuit.
Our house was built in 1955 and we had this problem when we first moved in. No smart equipment at that time, but lots of other stuff including blenders and hairdryers. and a space heater.
Over time we ended up adding three new circuits and now we don’t have any of those issues.
- automations. The one that @bry is referring to is that Alexa can create “hunches” which guess what you want to do and then offer to set it up as a regular routine. The offer is made verbally and it’s way too easy to say yes to, in my opinion. These don’t show up in the regular routines section of the Alexa app, but they are in there, so you can check to see if any were created unintentionally.
https://www.amazon.com/gp/help/customer/display.html?nodeId=G7F5F7K93GKSLC4F
I don’t know whether Google has a similar feature or not.
Another automation possibility is a presence based automation based on a phone, and you are turning the phone on and off causing the system to think that you are leaving the house and coming home again. But most people figure that went out pretty quickly.
The easiest way to diagnose The automation issue for zwave switches is to disconnect the hub from power for a night. ( also take out any batteries if it’s a V2) if the lights still go on and off, it’s not likely to be an automation.
(There’s a small possibility that it’s zwave direct association. We had a dog who used to steal remotes and chew on them, which could cause a lot of random poltergeist activity! 
but from what you described, I don’t think that’s likely unless you have a single remote that controls all of those switches.)
- cloud glitches. These can happen, although they aren’t usually repeated multiple times. The most common issue is an automation being delayed and then running several hours later. But sometimes they can just apparently come out of nowhere. If this only happened one night I would think that might be possible, but if it’s happening every night, I think it’s more likely to be 1) or 2) Still, report the problem to support if you can’t find anything else as they can see some things from their side that we can’t.
Good luck, I know these are very frustrating. 
- One other possibility I will mention, although the first three are much more likely, is drone activity. Some drones do operate in the same band as zwave, and one flying near your house can cause drop off issues for your own equipment. But if it’s that, it will be many different kinds of Z wave devices, not just light switches. And quite commonly it will start on one side of the house and then be the other side of the house. This is a real issue, and we have had a couple of community members affected by it, but it’s still pretty rare. So it would mean that either you have a neighbor with a drone or you have a city government with a drone and they are flying near you. (Or in one case, a community member had an issue with his own drone that he brought in the house to recharge.) But see if you can eliminate all of the other possibilities first, and then we can talk about this one.
