On my Rancilio Silvia and Faema MD3000 I get pretty consistent flow rates. I dialed in for my favorite bean to deliver a 35g shot with 14g of coffee in. It pretty consistently comes out in 25 - 30 seconds. Since yesterday, with the same grind settings it takes about 40 seconds to pull 30g. The 5 shots I did afterwards all took about this much time. I literally didn't change anything, and also the pressure (I have a manometer installed) didn't change.

I know there are some variables that might change the flowrate a bit like outside temperature, bean age or air humidity, but this sudden jump seems extreme.

Any ideas?