Re-did my kitchen maybe 5 years ago, and when I pulled the counter away from the wall discovered a gap ~1½" between the floor and wall. No wonder my wife was complaining about drafts!!

Did the same as you...blocked it off, and filled the space with expand-o foam. There were also a bunch of holes in the floor, probably for gas, plumbing, etc. once upon a time. Glued dowels in to plug them too before we put the new floor down.
Gotta love some of the hack "tradesmen" who'd been there. Whoever put down the flooring for the PO, couldn't be bothered to move the stove, just cut the linoleum around it.