I have read in other threads that LH does not open up *A award availability for premium classes on long haul routes until about 15 days prior to flight date. If you go to the *A website, it indicates that to book an award flight on *A partners that you must do so by going to the website of your mileage program ( in your case MP/UA) and book via their award travel booking process. I have been wanting to book a flight on LH using MP miles and it has not shown any LH availability on the UA search engine since I started looking several months ago. I do seem to recall seeing Economy availability, but don't have any recall about PE.