I think your new photos show that what I thought was a concrete lintel in the first photo, is really the edge of a concrete slab?
EDIT: or is the lintel supporting that concrete slab?
Do you know what's above the slab?
As I said before, I am only a DIY'er and may be very wrong, but your photos suggest to me that the wall was at some point load bearing (and may probably still need to be!).
At the very least, the corner of that slab (or lintel) needs proper support.
I think getting in a structural engineer may be prudent, but that's just me
If you want some further advice on here, you may want to ask the mods to move this thread to 'building'