Are you talking about the itinerary that has the 55 minute connection in the morning? If so, I'm able to book it and can see the booking class.

EDIT - I posted an image but then I realise it had changed the dates of the flights - without telling me - when I clicked through to the final page of the dummy booking.

It seems LXS-JIK only operates Saturday and Monday and JIK-ATH on Wednesday and Friday in the winter. There are more flights looking forward to next June but it's only a 30 minute connection and I can't find any site that'll let me book it. What dates were you looking at?