Thanks for the tips.
Making changes within the app, no error is shown but the changes don't stick after saving, from website the below error is returned
For technical reasons, your seats cannot be changed online. Please contact our Service Center.
(D/G - Not windows)
Will try calling again, HUACA if needed.
No stress LX reserving seats for SEN, but I do expect to be able to have seats together considering the whole front row is available, not unreasonable? Both pax on same ticket.
Edit: They will not relent, has to be done at airport. I'm looking forward to flying Swiss, but this first experience is rather annoying (I totally appreciate 1st world problems) Flying LH F on return, can select any seat I like.