It's mostly about your repeaters. This topic is a bit old but as far as I know is still the best place to find repeaters that people have mentioned to work well (there are not a lot), as well as related discussion:
I said "mostly" because the hub plays a similar role, but Hubitat made a change early on in the C-3/C-4 that allowed these to work when directly connected without "falling off" that has carried over into at least the C-7, as Zigbee is the same (aside from internal vs. external) in all. It's possible the C-8/C-8 Pro (which has newer Zigbee) may have inadvertently changed something here if you have one of those, but I don't remember hearing anything in particular.
