One more angle. Sometimes Alexa says offline while the device app still works because the cloud status lags after a brief Wi Fi hiccup. If you can control the plug in its own app right away the Alexa side will usually catch up in a minute or two. That said, the root cause is almost always the router doing something clever at night, so keep 2.4 simple and fixed, stretch the DHCP lease, disable scheduled optimizations, and update firmware on both sides which, yeah i did those and the overnight dropouts vanished, and I did not have to move the router or anything.
