Mhm, its hard to tell, maybe some other folks have opinions on this... in the third picture, some joints do not seem to be soldered/tinned...
Also for stability reasons, i would solder the stabilizers of the rotary encoders to the CS PCB.
You said that you have tested this CS with another baseboard, that works fine with another CS, therefore the problem must be on this CS (Sherlock Holmes :-)), not the resistor networks (which i assumed in last mail).
You can always try cleaning flux with alcohol and a toothbrush, sometimes it hides very tiny bridges.
Best regards,
Peter