I had this happen with NowTV some days ago for the first time. Though like you, I've only started using WIFI few days ago after moving flats and not having my router next to the PS4 anymore.Bit of an odd issue, grabbed a PS4 a few months ago, all working fine set up in the living room, moved it up to the bedroom recently and having to use WiFi rather than a cabled connection.
I can play games for as long as I like over WiFi, but when I go to download a large file say an update or try to stream something in HD say via Netflix or NowTV it will freeze after a few minutes. The console is still running, but the controller will disconnect and won't pair back to the console. I have to hold down the power button for a good few seconds to do a full reset rather than go into standby mode. It will then boot back up fine, controller works fine.....
For me this happened after I set the controller to go disconnect after 10minutes of idle while watching Game of Thrones and the NowTV app seemed to chrash. Hasn't happened again after I disabled controllers turning off from the powersaving features.