I reported several cases like this, I remember a case in MP Two Villages a building tile that tanks and vehicles can move and fire through, so, I think one thing is the image you see on the tile and another the effect on LOS.
I'm guestimating that either there is some sort of HIDDEN element that maybe got added here during the scenario creation, or there is some LoS glitch that maybe is due to how the vision-blocking terrain is set up on the sides of the squares involved. I keep running into this issue constantly when my opponents insist on making a push for the fort