I see the OpenVPN Interfaces is your PIA stuff.
So I've just read through your problem again, you had your Site-to-Site connection A/B fully working and the problem with A can't access B started with adding PIA as OpenVPN Client, right?
Generally speaking for most scenarios with VPN providers you want to enable the Don't pull routes option in your OpenVPN client.
Also check out https://www.netgate.com/resources/videos/openvpn-as-a-wan-on-pfsense.html - very great hangout! Maybe you can grab some useful tips & tricks for your PIA.
Troublesome could be your any-any Firewall Rule in the OpenVPN Tab. You allow any traffic PIA is sending in your direction there!
-Rico