If you look closely in the video, when he extrudes, for a split second when he hasn’t moved the extrusion, the mesh looses the bevel, same as it’s happening to you. That’s probably because of parts being too together. So there may be a couple of things happening, first check if you applied the scale on that part, the modifiers may be misbehaving because of that. Also check if you don’t have interior faces around that part, you may have tried to extrude and then tried to undo and didn’t go far enough and left some faces there. So change to face mode selection and check for interior. Also you may have so double vertices, so in wireframe select vertices all around that area and M to merge by distance. See if any of that helps. Also try expanding the shape a bit, so there isn’t any Z fighting.
