Doudini
After some more tests I noticed that the Brush Tools dont work correct on Unclosed Geometry. After doing polyfill the brushes lift option and surface brush work. Smooth brush still seems to have issues and I miss Wacom Pressure options to control strength etc. (I know can customize the wrangles inside the guidegroom) But there should be some better default artist friendly options.
Also I Hope one day houdini will get a real brush engine instead of faking things with the stroke SOP, The paint SOP could need some optimization too, espcially for wacom tablets. It feels very limited and clumsy to change settings etc.
I'm glad you found that this was partly due to open geometry. This is probably something we can fix internally, as most operators that rely on generating VDBs (as these do) should close the geometry as a preprocess step.
We do have some limitations still with the stroke SOP & state which we hope to address. But the tools that are in place should of course work out of the box, so please report any remaining issues as bugs.