Sorry to dig an old post, my point here might help others.
According to this post from @Pepe that cable placement seems incorrect when running both cards in 2.4Ghz mode.
@Pepe can you please confirm this image (which @Julian_Zimmermann received from Turris support) is incorrect? If so, what’s the suggested way to switch the cables? I believe the only way would be to also disconnect the cable from the diplexer, but it seems it needs more force than to disconnect from the wireless cards and I don’t want to mess it up.