I was playing "Whole Lotta Stratis" MP mission (not sure if this has impact). At the starting location at the depot east of the city at Agia Marina.
With the NLAW equipped in the green lookout tower near the main entrance, when you walk to the walls you can fall out. With a rifle or pistol out you're ok.
The wall will stop you from moving out of the tower, until you release to forward move key (default 'W'). At which point you fall through the wall.
I tried this in the green modular building right next to the tower and there was no problem.