you have two battery powered Zigbee devices and no mains powered Zigbee devices other than the hub.
It’s very likely that they are simply too far away from the hub and sometimes lose connection. 
The hub is a plastic box That includes multiple radios, typically including one for Zigbee and one for Z wave. The Zigbee radio creates a Zigbee network. the zwave radio creates a zwave network. The two have nothing to do with each other, except that they both connect to your SmartThings account.
Zwave utilities will not affect zigbee devices.
It sounds like in your new home that you probably need to add A few Zigbee mains powered devices to act as zigbee repeaters. Even just a Zigbee smartplug will do.
The easiest way to test This theory is to move the current Zigbee batterypowered devices back close to the hub. If they stay online, then, then the problem is the physical location. (For the test, choose a location close to the hub, but not too close. At least 12 feet away, but less than 20 feet away. It doesn’t have to be clear line of sight unless you have unusual architecture features like stucco walls or foil wallpaper. After you read the range FAQ, you will understand better.)
It would probably help if you read the FAQ on range and repeating. Although it is old, the information is still good. Start with post 11 in that thread, read that, then go up to the top of the thread, and read the whole thing. I will link directly to Post 11.
A Guide to Wireless Range & Repeaters - #11 by JDRoberts
(There are a few other things that can cause this problem, and it might be a Wi-Fi interference issue, but from your description I think it’s more likely to just be range. )