That 2-2.5" of rain could cause additional FC loss.
I am more concerned about your cartridge. As you can see from my signature I too have a cartridge filter. Could it be that your filter media has a tear somewhere? Allowing unfiltered water to blow back into the swimming pool? The first year I came to TFP, I completed a SLAM, but after a week and a half my water was not getting clear. I held my skimmer up to one of my returns and low and behold stuff the filter should have been catching was blowing back into the pool! The cartridge was several years old. I bought a new one, and my water was clear in about a week.
Is your pressure going up over time?