It usually means the operating carrier (if not LH) credited the flight to their own Frequent Flyer program or (if LH) credited it to another airlines FF program.

This has happened to me a few times when I fly on United but want the flight credited to my Miles & More account. Since your boarding pass clearly shows the LH M&M number, you *should* be able to persuade them to properly credit the flight to your account, but it may take some time since M&M may have to get the other program to correct their records and back out any credit they gave on *their* program before M&M can give you credit on M&M.

Good luck!