I had this on a flight to SIN a few weeks back.

Was booked into 1A, but when I got to the gate they advised me I'd been moved to 2E - not what I wanted.

I didn't argue with the gate staff, but asked upon boarding. The crewmember said she wasn't sure about the change, and the CSD blanked my question. Once in the air, I noticed 1A heading towards the F galley, and I followed. He had a long chat with one of the crew, and I then butted in and asked if he was also crew - to which he replied he was.

When he asked why, I explained as a GGL member I was quite surprised to have been booted out of my seat for him. He was hugely embarrassed, and the CSD (who by this point had come downstairs) was mortified at the ongoing discussion.

It was all very jovial, but I did make a complaint to the GGL team a few days after the flight - and was told the seat was broken and wouldn't recline. When I countered by saying I had a photo of the seat working, and had had a long chat with the crewmember in 1A, they caved and sent me some Avios by way of apology.

M