My first answer is: no, it's a
TERRIBLE design. The beam pocket should not extend all the way through the concrete.
My second answer is that it was a mistake to completely fill the beam pocket. There should be space all around the beam, and the concrete or other material should not contact the beam on the sides and rear.
If the beam pocket is below grade as you imply, then the cure for this problem will be found outside, not inside. Excavate down past the beam pocket level, apply cement plaster parge to the bricks below grade, then two brush coats of bituminous dampproofing, and apply a waterproof membrane in the wet dampproofing, extending from grade to a foot below the beam pocket, and maybe two feet either side of it, and from the top of the beam pocket to within a couple of inches of grade. Just below grade, a flashing should be cut into a horizontal mortar joint, extending into the brick wall and at least 4 inches over the top of the parge coat/dampproofing/membrane. If it can be extended all the way to the back of the brick, it would be good. The flashing will help keep water from entering behind the parge coat and running down inside the wall.
It is also a good idea to completely remove any and all material that was placed within the beam pocket, and maybe this is best done at least in part from the outside, by removing a few bricks before applying the parge coat. There should be air space all around the beam (assuming it's a wood beam).
Architect (NY) and Home Designer (PA)