I had this problem, it's due to the timer relay forgetting how much time it needs to grind.
The only way to solve it is with half a kilogram of coffee going to waste,
You set the coffee amount MAX and set the coffee size to MIN clean the trays for water and grindied coffee and start making around 20 coffees one after the other immediately get your phones timer, and measure each time you make coffee how much time it takes to grind you will start from 5 seconds probably, eventually after the 20th coffee it will be 7, and do it until you reach from 11-12 seconds, hope this helps you, it helped me.