Looks like you're good on 2.15 then. Disregarding all the Blues for a moment, do you have a good physical layout/spread of other mains-powered zigbee devices so that your zigbee mesh is strong across your home's footprint?
I haven't looked into it any further since, but I remember not being impressed with my Blues being reliable repeaters when I put them in. It's not a big deal for me since I already had a strong zigbee mesh in place.
But if you're relying on the Blues alone to maintain your overall mesh, perhaps sprinkling in some high-quality zigbee-3.0 mains-powered repeaters might help. Or it could just be a different wild goose chase... Just trying to think of some other considerations here.
The only other zigbee devices are hue bulbs around the house. Approximately 100 or so connected to 3 hue bridges.
Yesterday did a test of about a dozen blue switches very near the Hubitat hub. All paired. All fell off as of this morning.
The Hue bulbs don't count in your Hubitat mesh because they're paired to a different ZB controller (Hue bridges).
My suspicion is that you need some other mains-powered ZB3.0 devices to beef up your Hubitat ZB mesh, but I'm leery to tell you to try that, since they'd be more devices to buy, and I know how this stuff can really add up.
But an option to keep in the hip-pocket as you continue to diagnose with Inovelli... If you go that route, the Aeotec Zi is a good repeater, and many folks here really like the Tuya ZB3.0 USB repeater device (plus, that one's inexpensive). You'd want to space out enough repeaters to cover whatever 3-D home footprint you need.
At this point I’ll try the repeaters. The price point does not outweigh the unhappiness of my wife that the switches are not working. 
Are your hue bridges on the same zigbee channel as hubitat? That will certainly cause an issue.
Hubitat. 20. Hues. 11. 11 and 25.
