While sculpting a hand dyntopo stopped working after I unionized the last Finger to the hand. It worked for the first four, but after the last it didn't. It shows that it is activated, but it just doesn't add new geometry. I already checked for geometry inside the mesh after the union, but there isn't any. Anyone got an idea, why it is not working?
If anyone is still having this problem, the way I fixed it is to use the Snake Hook Brush. Make sure Dyntopo is enabled, and then just press wherever you need to make the mesh denser. There's no need to actually pull anything around – just tap and it subdivides it all. Hope this helps at least someone.
Here's a way of resetting the interface (including sculpt tools) while leaving the actual model alone. There are a lot of tools and options (A LOT) with sculpt mode, and sometimes it's easier to just reset everything to factory mode like when you created a new model, but without actually opening a new file.
As of Blender 2.92, go to the Edit→Prefrences menu. Make sure you're on the Interface tab. In the bottom left corner of the window, there is a hamburger icon. Click on it, and select "Load Factory Preferences".
This is an important last-resort move to know when your interface has gotten too out-of-hand to correct manually.
As a caveat, though, this also resets some system preferences, like switching your Cycles render device from CUDA or OptiX back to None (CPU only). This is an infrequent enough thing, and easy enough to fix, that having to change it back each time doesn't bother me so much.
I had this same problem. Try checking Refine Method. If it is set to Collapse Edges it can only make a mesh less detailed, you therefore have to swap it to Subdivide Edges or Subdivide Collapse. I believe Subdivide Collapse is the standard setting, but it got changed by accident.