Framing Identification – GreenBuildingAdvisor

Can anyone advise what the purpose of these framing members are and why they have a top plate notch missing?

They are across the room from each other and aren’t electrical chases. 

Any harm in filling in the missing top plate before rigid foaming the rim joist?

Separate question:

In voids behind corner studs such as in the last photo, is air sealing that crack going to create any problems from a condensation standpoint? I can’t get any insulation in there. 

The exterior wall of the corner is sheathed with 1/2” perforated foil faced foam in climate 4A.

Thank you. 

Thanks!