I have had the best success w/Zigbee devices on my hub connecting to the hub via repeaters, rather than direct. I run Aqara on my C8 and C7, and they are solid on both hubs. I use SonOff USB Dongle repeaters, Ikea repeaters, Centralite/Iris repeaters...
I'm at power level 8 channel 15 on the C8. Things are working there so I haven't futzed w/the power in a while, higher powers did not help. So generally I'd go lower as long as things stay connected/work normally.
If you continue to have problems w/the Aqara I don't think you can go wrong trying adding a SonOff USB Dongle P repeater. Takes a little work to get set up, and ugly as sin so you have to hide it, but it's kept things in order for me.
