I've had my 3 deco mesh system for a year or so. The last couple of months one of the X60 routers keeps switchinf from green to flashing red. It will occasionally switch back to green but mostly stays red flashing. I've tried factory resetting multiple times. It does seem to be quite warm (bording on hot) if I touch the top (contrary to the others).
I have two ethernet cables connected to other routers (i.e. providing connection to two laptops, internet phone). Having said that, disconnecting those makes no difference (i.e. it will be green for a couple of minutes then start flashing red again).