Hi @samh1b,
1. USCIS sent RFE on January 22nd 2021 and my response reached them on 3/10/2021. My passport was under renewal and they needed current passport copy. So I had to wait for it a little bit.
2. Company B had not started any greencard process, by the time my date became current in 2021, also I had not filed AC21 by then. So I left and immediately (at end of feb 2021) went back to company A (GC sponsor). Luckily my H1 with company A was still valid. I stayed with company A for a few years and worked for them on EAD in later years.
Then I switched employers and filed 485-j (supplement) with them. I am with company D working on EAD.
3. No. Company A never withdrew I-140.
Good luck for your case.