I am using HomePlugAV devices that have power-saving mode on as default but the problem is when they go to sleep they stay asleep. Nothing turns them back on without pulling them out the socket and pushing them back in again. There is nothing in the manual about turning off this feature. So I am using PING to broadcast packets on the 255 address every 2 minutes to keep them awake. I have a number of routers one being a Lenovo Newifi D1 on 21.02.0 and a Mi4C running 21.02.1.
finally solved the issue after some real hair pulling. In rc.local I inserted a line at the top "sleep 30". My guess is this Mi4C containing the 7628 being a slower CPU than the twin core 7621 in the D1 causes a race condition on boot. Inserting sleep 30 as the first line in rc.local allowed PING to daemonize on boot. I think adding sleep 30 as the first line in rc.local might be the first config I add to all my routers from today onwards.
.# Put your custom commands here that should be executed once
.# the system init finished. By default this file does nothing.
#papdee: just sleep a while so system can complete startup scripts