I understand the delays are frustrating, this is why I finally got myself a Zigbee sniffer and learned how to use Wireshark so I could finally see what was actually going on but thats a steep curve I'll admit!
Since 6C isn't on the list of bad RF modules we'll assume that isn't the issue.
Since I can tell you that with 10 Inovelli Switches (and a dozen or so Hue Zigbee bulbs also directly on the hub) my button presses and actions are fast enough to look local.
So the next question is, are all events being delayed (ie. on/off updates to hubitat) and how fast does it respond to a level change command from hubitat (until you see the LEDs change)?
I.e. is there a general lag of Zigbee command issues or is it just one-way,
Then I would take a look at the routing data from the hub at http://X.X.X.X/hub/zigbee/getChildAndRouteInfo (where X.X.X.X is your hub IP) and then at this thread: Making sense of this Zigbee Routing Table Neighbors - #2 by Tony
Look for your Inovelli Switch, is it listed as a neighbor (with a high LQI and low cost?) or is it listed as going through another router and if so, check the LQI for that router device.
Hope this gives you a direction to look to diagnose your Zigbee issue. While Zigbee in theory should route around problems, in practice, there is a good chance a badly behaving (or weak) router can have significant issues. Sometimes, just rebooting the offending router device can fix the problem (at least for a while)
