There’s a little black button on the back of the router, press it once and one of the wifi lights should come on, press it again and both wifi lights should come on.
To answer your question, maybe it’d been knocked? Maybe someone thought the wps worked by pressing once rather than pressing and holding?
Thanks. The black button on the back is a power button, but there is a white button on the top which turns the wifi on and off that I didn’t realise was even there. Its possible it got knocked. Will see if it reoccurs.