There are a few reasons that DF64P or DF64E is having issues with grind size adjustment. I am going to walk you through the steps one by one.
1. The top burr isn't seated evenly.
The wood cover for DF64P & DF64E comes with 2 screws. If you open the wood cover and check the burrs there is 50% chance that you might put back the wood cover incorrectly. Please follow the following photo to make sure you install it correctly.
Also when you tighten the two screws on the wood cover please make sure you fasten those two at the same pace so that the top burr can seat evenly.
2. If above step doesn't fix the issue and you are still getting coarse grind even if you adjust grind size to single digit. Then it might need to check grind size dial zero point. Manufacturer might have mis-adjusted zero point. Please follow the following video to re-adjust zero point.
3. Align burrs
Align burrs using shims