I’m having this same problem actually but it doesn’t have to do with connecting to a WiFi network. I’m running NZBdrone off a hardwired Win 7 server.
It happened to me first last week when downloading the first episode of South Park. I have some of my shows set to only download WEB-DL files (prefer the quality and don’t mind waiting). Anyway, after a few days, nothing had downloaded so I checked manually for a file. There ended up being a couple of WEB-DL releases posted days ago. I thought it was odd but manually grabbed it and it downloaded fine.
Today I check and see that New Girl hadn’t downloaded either. I manually searched again and saw that a WEB-DL was also posted - same for Brooklyn Nine Nine.
Any ideas on how to fix this? I did a manual RSS Sync and neither shows were pulled.