The machines grind will change by itself, either from leftover grinds inside the filter/dispenser or due to an inadequate bean amount dropping into the grinder beforehand. All are resulted by the machine itself and it’s up to us to switch the grind. If the grind becomes a little too coarse, the water will run through it faster and will extract less coffee concentration /espresso and it will affect taste. However if the grind is too fine the taste will become bitter and more intense. Coarser grind tastes worse tho. I believe the lower the number the coarser and the higher the number the finer. However if you run the machine to just keep dropping shots it should fix itself.

The weather can also affect the grind, something I learned at the first coffee shop I worked at.

Make sure your espresso is full, decaf and regular espresso beans. The weight helps the machine to remain calibrated. If it is pulling shots slow, you can calibrate the shots by pulling 2 espresso shots at a time. Until it is running between 18 and 25, this works for decaf and regular caffeine. If this doesn't fix it check your Equipment Cleaning and Service Manual. Good luck.