My sertraline brand has changed and I'm experiencing anxiety symptoms again.Anyone else had this?

Hi, harry!
I'm guessing that you're using generic products? While the amount of the drug is the same in each different generics may use different inactive ingredients as fillers, binders, colouring agents, etc. These can cause some people to not absorb the drug like they're used to.
I'd check with your doctor first of all to be sure you're not experiencing breakthrough anxiety for some other reason. Then, if your previous prescription worked well, ask your pharmacy to special order that product for you. Most pharmacies will do this although you may spend a few cents more for it.