Did you ever hear back? I am so sorry you are having the same problem. Please if you don't mind keep me posted on if you get a response and resolution! Also did you call or email?We are having the same exact problem. Had the lid for about a week and the sag is the same as yours and ours has the center support bar.
We have contacted them and sent pics but they are requesting even more pics with “natural lighting” which is hard to get right now.