This started happening several weeks ago. I routinely reboot my RPI 3 after a kernel upgrade. Lately, I can't ssh into it after a reboot. The error is "No route to host".
Curiously, I can attach a monitor and keyboard, pull the power on the Pi to force a reboot and it always comes up to a login screen.
I can disconnect the monitor and the keyboard, ssh in and reboot and "No route to host" again.
Ideas anyone?