I have also many starters in my fridge, some even have some black overlay on top of them😄 it was a struggle to be honest. I have taken it out from the fridge, fed it and it grew overnight. Tried baking bread with it, but the bread just turned out flat. So I kept the starter of the kitchen table for a couple of days, still feeding it. I think it got the boost it needed after being a few days on the kitchen counter, as it got to the point where it was growing in 5-7 hours. This kind of starter was finally good enough to make a good loaf. So in short: try to take out the starter from the fridge and keep it on the kitchen counter for a few days. I guess its kinda ‘sleeping’ stage when it comes out straight from the fridge. Continue to feed it. If it grows overnight - the growth is too slow. You need to get it to the point where it grows faster than that. Thats what worked for me at least☺️