We have certain ad set settings and creative that we consider as a baseline and we test it with new creatives/audiences.
It is the baseline for a reason. It provides us with either good or satisfying results.
We stopped using it for few months due to an inventory shortage. Once we got back, the cost per action in our campaign increased by around 40%.
CPM increased by 70% as well, so we're assuming that the auction got more competitive but our creative's performance didn't change much.
What can we do to adjust?