The door does stick a fair bit after periods of heavy rain. When I stripped it and re-painted a couple of years ago, the bottom of that side of the frame had completely rotted. I used a wire brush to get rid of the loose material, then fixed it and built it up back to a door shape with epoxy filler. Clearly only a temporary fix. The door and fame are massively exposed to the elements, and we have a flat roof above it that drains off in that area, which is the root cause of the issue. I had to do a similar bodge on the bottom of the panels covering the frames and the sill (see before and after photos from last time) although I did let in some new pieces rather than use filler for everything. The sill has now completely rotted again. It sits directly on top of the flagstones with no membrane underneath it. It needs to be completely replaced to be honest.