That’s an almighty build up SteveBRS!
How long ago was your last clean? I take it wasn’t the 10 to 12 days you mentioned?
Do you moisten the beans or is the environment humid?
He only time I’ve noticed shifts like this is sometimes due to the weather. For instance, during the heatwave we had in the UK, I noticed I had to grind finer, and the same was true for other grinders I had in the past. Otherwise the little Zero is very consistent.