My dress breaks between the legs while the sim is walking

Hi. The mesh is vertex painted with the wrong color, 02FF02, everywhere. It should be 00ff00 everywhere but the skirt. You can edit the paint manually now as shown in the linked post above but in the future just transfer it together with weights and uv_1.
Also, it is best to let s4s create a blend file and work in it instead of importing the garment into the blank scene. Just export the reference, import the garment there, adapt it, leave the rig and all body parts as they were.
(the process is the same in blender 3+)