I migrated from a C7 to C8 and the migration process seemingly went without a hitch at least on the surface. Then the problem started with zigbee devices constantly losing connection. The connection diagram shows multiple connections for all these devices but no data is being received. Power-cycling the hub or the devices do nothing and I'm forced to remove then re-pair the devices. Then a day or to later the connection is lost again, rinse and repeat. I'm spending so much time on trying to keep the mesh up. Changing to a full-wave antenna doesn't help either.
Now I'm regretting moving from C7 to C8 and am considering going back to C7.
Edit: Most devices dropping off the mesh are Hue motion sensors (which people have reported), but also includes other types of zigbee devices such as contact sensors, thermometers, and shades.