There are also weep holes in the bottom of the outside stucco flashing. If they get plugged,usually by sloppy stucco installers, water could back up and drain inside. Or, there isn’t a good ‘z’ flashing to keep outside water off the slab.
However, I’d look closely at your door. Bet that bottom threshold is missing caulking when installed.
Be sure the edge is sealed as well. ie weatherstrip on the vertical and top sides
