I had to take half the door latch off the shed and move it over a quarter of an inch (took thirty seconds, just three screws). I think that it was a little tight to start with, and then the weather and the structure settling slightly was all it took so that the two parts would no longer smoothly fit together.
I was in the shed today, despite the rain, continuing to clear stuff from my back room. I’ve started building more things into the shed – just some crossbars to hang tools right now; soon enough a shelf or three to take advantage of all the space – so it won’t become cluttered like the rooms it is decluttering.
Finally, checked the sump pump today and found that the hose had shifted and blocked the float just enough that the pit wasn’t draining (it was actually overflowing onto the floor). Moved things around a little and it’s draining fine now, but I think this and the frozen hose the other day are signs I should finally go get some PVC pipe and properly build out the pump line.