New answers tagged structural
I would knock that sucker out with impunity. If it is to serve some purpose, it most likely would not be code compliant. Fire blocking is the first thing that comes to mind, but it is only in one stud section.
You are most likely referring to Cross bridging or blocking. They must be installed to keep the joists from twisting.
Usually the HVAC subs knock them out and leave them out, but if you place something like a 1X4 or heavier between the 2 joists at the bottom, it would stabilize the movement of joist deflection. Make sure it is a tight fit.
It's time to take photographs, measurements, and contact the association. Take measurements periodically. Check other windows & doors for similar problems, and ask your downstairs neighbors about the same. The HA needs to get to the bottom of this, and only they can do it.
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