When you say "LAN-to-LAN link." you just mean some form of point to point L2 connection?
So you have an interface on pfsense that you put some transit IP range on - see attached simple drawing.
So you are not natting to this transit? Are you using any transparent proxy on either pfsense on these interfaces? What are the firewall rules on these interfaces on each pfsense, on the transit network, any sort of floating rules? What is the static routes you create on each pfsense for the different networks.. I assume your routing is correct since you say all works other than 80..
Maybe issue with using a proxy, or your natting? Always helps to have the full picture of the setup to try and figure out what is not right..
yournetwork.png
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