With the updated WSL version out I probably won't ever run across the issue again. I can't remember the exact circumstances, I may have had the folder open in a window or something (thinking of it, Windows doesn't let you rename files out from under processes, which may have been the reason).

However I do recall that trying to ctrl+c kill it didn't work. I don't recall what else I had/hadn't tried; I was rather busy at the time and couldn't stop to make a proper bug report.

All that mattered to me was that it completely stalled for no transparent reason and my best option was to just not even try to do real file management from the WSL environment.