Sometimes this can be fixed by pausing and resuming, but usually I have to exit qbittorrent and restart to get them to not be stalled. The symptom is that there are many active Seeds and many active Peers, but 0 Down Speed and Status is Stalled. I get downloads randomly stalling (often when they are first added to qbittorrent, but sometimes after they have downloaded some portion already).
Stopping and restarting qbittorrent usually (always?) causes these torrents to either recheck or download a last few bytes (not sure which action is happening - it is too quick) then complete successfully and switch to seeding. Pausing and resuming does not seem to help.
I am having the same problem as well, running qbittorrent 4.0.4, but there are 2 symptoms: