There is an inconsistency as to which walls can be used as cover, but it's unclear if this is also the case on the live game (not about to try to get to floor 95 again)
The pillar in this screenshot CAN be used as cover, but the wall sections on either side of it CANNOT. This is annoying as the section to the left leads up to a corner.
The pillar in this screenshot CAN be used as cover, as can the wall section to the left. However, the wall section to the right CANNOT. This isn't a big deal as the section on the right is near a spawn door. However it does demonstrate inconsistency as to what can or cannot be used for cover.
Most frustrating of all, this wall CANNOT be used as cover.
Other players in the group confirmed they couldn't use the same walls for cover, so it's not an issue with my keyboard controls.