These are almost certainly the source of your problems. See a few sources for more on this:
- Hubitat "Zigbee tips" docs:
Avoid adding Zigbee lightbulbs to your hub in combination with other Zigbee devices, since the lightbulbs will try to act as routers, but unfortunately they only perform this role properly with other lightbulbs. The exception we have found are Sengled Zigbee lightbulbs, which do not try to take on the role of repeating other Zigbee devices. Zigbee light bulbs do not have issues routing among themselves, therefore a good alternative is a separate Zigbee network via a compatible bridge such as the Philips Hub Bridge, or a second Hubitat Elevation hub with only Zigbee lightbulbs paired to it.
Several forum posts and threads about these and a few other problematic bulbs, though there are few directly-paired bulbs I'd trust regardless:
- Not all bulbs are created equal
- Zigbee Light Issues - #4 by bertabcd1234
- Sylvania/Osram RGBW Bulbs - #2 by ogiewon
- many more you can find with a search on both here and other forums
People usually don't like to hear this, which is why I'm trying so hard to prove with multiple sources above that I'm not crazy for saying this. 
The bad news is that this is the truth regardless and very frequently the source of these problems. The good news is that you already have a Hue Bridge. My suggestion would be to pair the Cree bulbs to the Hue Bridge, keep the ST plug on Hubitat, and consider adding other repeaters (like the ST plug or many others--just not bulbs) on Hubitat if you need them for the range or number of devices you have. The Cree bulbs work great on a Hue Bridge, and you already know Hubitat has an integration that works well for these.
My guess is that when you move these off of Hubitat, everything else (just your ST plug, I suppose, unless there are more devices you didn't mention) on your Zigbee network will work well again. So...mixed news, but hope it's at least helpful!
