Please look at the images one by one and try to tell me what's going on. This is not the first time something like this happens to my mesh.
????
Please explain why this happens. I cannot make a table for a 3d model of my room. It's an assignment for one of the course here (Fundamentals Track)
My guess is that the bottom of the table and the top of the leg are z-fighting, and blender doesn't know where you are wanting to cut.
A quick fix for this situation would be to hide the bottom face of the table, add your cuts, and then unhide.