I recently got a 5lbs bag of Red Bird espresso blend and was blown away by how good it tasted. For about a week, every cup was near perfection. So I reordered but this time only 2lbs. Same grind, temp, flow etc... but now, the coffee has a kind of acidic bitterness (sorry I'm not good at describing what I'm tasting) that I can't resolve. Is it possible I got a bad batch? Should I have to make more than minor adjustments between batches? I've already ordered another bag to see if things improve because I was so blown away by how good the first batch tasted.

Any coffee can vary from batch to batch, roasting is not easy to be 100% consistent. So batch to batch can vary but should keep a similar profile if the roaster is good. Try to dial each bag you received. Then, from day to day or even hour, you'll just need to make small change.