but it also fails when there are blocks that are not uniformly scaled
(even if they do not contain solid hatches)...
Solved, it is a problem that has always existed in AUTOCAD itself, that is, there is a deviation in the SPLINE bounding box.
Ordinary SPLINE, API has been solved,
However, in the block, the method of finding the bounding box is to use ARX's AcDbSpatialFilter::queryBounds(...) method, but there is still a problem.
Now I use my own method to process SPLINE in Block separately.
The API has been updated, please try downloading it again.