Established starter suddenly not rising
Hi, I've been using my starter for about 6 months now with good results. I bake once a week, feed the starter and keep it in the fridge until 2 or 3 days before baking again to give it time to build up. Last week I took it out of the fridge as usual but perhaps took a bit longer to feed again (normally I do it within a few hours of taking it out of the fridge but this time it might have been 8-12 hours, not sure). It didn't rise at all. I've had a busy few days and couldn't deal with it so decided to take some of the starter I froze recently, just before going on holiday. I fed it as soon as it thawed and 24 hours later absolutely no rise at all. What could cause well established starter to stop working? Do I need to start from scratch or just keep feeding this regularly to see if I can get it started again?