When I load the silly object in the picture (a single Dynamesh volume with 2.3 million points set at 1024 Dynamesh resolution) and split the pink blob on the right side off into a separate subtool, I get a pink blob with approx 250k points. If I re-Dynamesh (hold ctrl then click and drag in the work area) this new subtool, at the same Dynamesh resolution of 1024, jumps to over 1 million points. It did not used to do this. In previous versions the new subtool would re-Dynamesh and would have a point count close to it’s original count, 250k or so. I get the same results on two different machines one of which is a clean install of ZBrush. I am using version 2021.6.1. Am I missing something or is this not functioning correctly?
Hello @bjackson
There is currently an issue related to Dynamesh resolution under investigation. If you would like your specific scenario to receive attention, please go to Pixologic Support, and start a conversation there.
Thank you!
I too have noticed this issue and found it an impediment to my workflow. I am struggling to understand how it improves my Zbrush experience aside from isometrically excercising my jaw muscles through increased tooth gnashing.
Solved: If an object is smaller than 1x1x1 world units in size (Tool: Size submenu) then a multiplier is applied to the dynamesh resolution calculation. If you scale your tool to a size where all subtools are larger than the 1x1x1 limit then Dynamesh behaves as it did before the update.
ZBrush tech support 
btw.