LX 4402 (so a LX ticket) but actually EW boarding pass for DUS-ZRH-DUS.
Easy access with UA Platinium in DUS (small lounge BTW) but I had to show my MP card.
A little more complex at ZRH as I had to show indeed the LX ticket information (but mainly so that the lady could enter the LX flight).
Fast lane access at DUS & ZRH were granted.