It was working great up to and including your gig so maybe something moved while in transit on the way back, with the arm attached, in the gig bag. I almost always remove the arm and place it in the side pocket when I am done for a while. Feel safer this way. Don't give up on it. If after your settling in time period there is no improvement you can always have it looked at by someone who knows, if such a person is local to you. As previously said, I have the same model. Bought mine slightly used too, at a bargain price. Really happy with it. Would still be just as happy had I paid full retail price new. Lot of guitar for relatively little money.
I am still mindful that you said it feels like there are two zero points when moving the arm up and down. And because of this I do not feel hopeful that it will repair itself in time. If it does then my next motorcar will be a PRS. Whatever the problem is it won't be much anyway.