Make sure your "Intersection Priority" (within your "Building Materials") is set to a higher number for the material you want to clean up. See attached
Robert J. Garand
ArchiCAD USA 28-Build 3110 USA FULL
Windows 11 Prof (64 bit) - Intel i9-14900K CPU 3.20 GHz - 64 GB RAM - NVIDIA RTX 5000 Ada Generation