This isn't a Hubitat issue, hence posting in the Lounge instead of Support... But if it needs to be moved, so be it.
I've noticed this more often in the recent past, as opposed to the last year or two, but when my Hue bulbs are turned off, they used to fade down over ~1 second or so. Now I see that some of them just look like the light switch has been turned off, shutting off immediately, without the fade.
Has anyone else noticed this? I haven't had a chance to inventory if it's specific groups / bulb types that are doing this yet, but it's a bit jarring when the light just cuts out without the fade.
I do have quite a few bulbs and dimmers attached to my one Hue bridge, but I do have a 2nd bridge that I have not used (it was a better deal to buy another starter kit than to buy the new color bulbs separately...), might it be worth it to try moving some of my groups to the 2nd bridge?
Just did a count on the About screen from the Hue app, and looks like I've got ~46 devices, between the bulbs and dimmers.
The default "fade time" for on to off actions in hue is 400 ms. How are you turning them off? With the Hue app? That should use the default. If you're using a third-party app, it's up to them what they specify (though if nothing, it will use the Hue default).
If you're talking about Hubitat's integration, for simple on/off commands, I think it just uses the Hue default as well (staff would have to verify what they're actually doing here to be sure). For
setLevel(level) commands, it will use the "transition time" that you specified on the device page, which defaults to a (for me) unbearably long 1 second. Apps can also use the
setLevel(level, transitionTime) variant of this command to override the default transition time (for that one command) to anything, down to and including zero. On Hubitat,
setLevel is the only time where this transition time matters, though a
setLevel to anything >= 1 on a bulb that is off will also turn it on, so could be used as a custom way to achieve a different on/off fade than Hue's default if needed.