Certain area in Research Facility still grey (spoilers for the corresponding location)

[lentinant]

In Biological Research Facility, there is an area with very long vertical shaft which you clear using Garm ability, with three sets of kinda "lung-shaped" rooms (the shaft goes in the middle of those). It is almost in the middle of the location.

I have fully explored the location, but this area is still grey. I don't have any icons for items or obstacles there. Neither I was able to find any secret areas in there - all surrounding areas are complete, and there is simply no enough room to fit secret space there. What am I missing here?

[Shyba]

check that shaft carefully for hidden walls

[lentinant]

Thank you. This is so far least noticeable secret in the game (even beyond the one in the water area).