My current employer is not the one who sponsored my I140 and I485. I changed to my current employer seven months ago and they filed AC21 for me. Now the company is not in a steady condition and I just received my green card. Do I need to stay in my current employer for approx. 6 months as people always says to avoid the trouble in citizenship application?
Once you have your greencard you are free to do as you please.
Consult with an experienced immigration attorney or make an info pass at your local USCIS when you need advise. Street law is rumor and "advise" you receive is based on someone elses case which may have nothing to do with yours. I consult with many persons on a regular basis who end up in deportation proceedings because they listened to street advise rather then consulting someone who knows.