Also....... Another thought.
Using your o/s... Find the name of an image file in the missing folder. Then, select All Photographs in Lr and do a txt search for the specific file name. If it finds the file name, right click and pick the option to go to the folder containing the image.
If the image does not appear in the search, then you know the image is not in Lightroom, at which point you will have to try and audit what actions you may have performed on the missing files or folders, inside and outside of Lightroom.