I had a similar issue to the OP with LH. I was booked DXB-FRA (LH, C), FRA-IAD on UA (GF) award.
Finally the DXB-FRA opened up with F on LH. I got UA to change that segment.
Checking with the LH website, never saw the change to F. Called LH, no idea about it.
Called UA, on hold, they couldn't make it work with LH, so they put me in GF on the DXB-IAD non-stop. That was nice.