Some seams look towards the end like the welding spots got longer

Possible causes:

1. Welding pressure:
   Is the welding pressure mechanically always guaranteed?
2. Upper roller:
   Is the upper roller touching the Z-bar?
3. Lower welding roller:
   Is the lower welding roller too low?
   Welding center must be in the center of Z-bar!
4. WEC-O3 circuit board:
   Change the existing with a new one.
   
   Attention: Make sure all jumpers and all little blue pontentiometers are in the same position!