The walls ends between the 2 scraps that you try to join are far from each other (1 passage is 10 m large, the other 20 m large), so even if you can join them, you will have strong distortion, like in the attachment.

Xavier has identified the problem here. It looks to me like a survey sketching, drawing or user interpretation of survey data error. The red lines are the undistorted scraps, and mimic exactly the shape of the scraps in the th2 files. The red scrap outlines can be seen to overlap significantly. Therefore, Therion has made a sensibly minimal morph to bring the scraps together (black lines). It is working perfectly. My first rule of joining scraps is to make sure they match approximately before invoking join, otherwise Therion will continually thwart your attempts. Step 1. Comment out the join Step 2. Make edits to the individual scraps so the wall lines nearly join Step 3. Reinstate the join Bruce