I have my parents booked in C on the WAW-MUC route and when doing a routine check on the reservation some sort of error/alert message came up regarding their seat selection.

I had previously chosen 1A+1C for them, but now both selections are showing up as unavailable for some reason. I understand there could have been an equipment change (not sure what it was listed as when the booking was made)?

LH's official seatmap shows a 1-1 alternating layout (1CD, 2AF, 3CD and so on...) whereas online it's 1-5 and just A/D. Any reason why both their seat choices are causing issues (1A should still be available, no?)?