I got RFE on employment with two items. One is where I am now (current company's location and starting date) and One is my sponsor information. I got this RFE is because at the time of filing 485, I already worked for my current employer, and I indicated that in my 485 filing. You don't have to do that at 485 filing. That is my opinion after going through everything and being worried. During the interview, the officer didn't ask me any ridiculous questions, just asked for employment letter, and I gave him my current company letter and he didn't even look at it, just put it away in the file. And that was it, the next thing I knew was that I got my green card.
I think the most important thing is that you get a "similar" job as soon as possible. That was the key to use AC21.
Good luck.