Although being somewhat experienced in setting up P2P OpenVPN on OPNSense for some reason this time I can only get traffic 1-way. It's been a while since I've done this so I've probably missed something.
Meaning, Site A LAN cannot reach Site B's LAN, even though Site B's LAN CAN reach Site A's LAN.
The OpenVPN firewall rules are set up the same on both sites: IPv4* Allow everything from everything to everything.
Protocol Source Port Destination Port Gateway
IPv4 * * * * *
OpenVPN Server Settings: (Site A)
Tunnel Net: 172.16.12.0/24
Local Net: 192.168.55.0/24
Remote Net: 192.168.54.0/24
OpenVPN Client Settings: (Site B)
Tunnel Net: 172.16.12.0/24
Remote Net: 192.168.55.0/24
There are no LAN rules on the Site B OPNSense other than the default LAN4/6 to Any.
I've been having the exact same issues.
I never had much issues getting OpenVPN to work with a passphrase configuration in the past, but as soon as I moved to a certificate-based tunnel I've been having the issues you've described, despite apparently having the correct firewall rules and routes configured. Traffic only flows properly one way.
On the reverse direction, Site B seems to be unable to exit the tunnel back to the LAN.
Have you ever figured out what was wrong in your case? Perhaps that would help me...