Having you tried turning it off and on again (after a few minutes)?
No, this is not a joke. Resetting the Roku box can fix streaming issues sometimes.
Why does this work? Like many set top boxes there is no proper power off button, just a standby mode. When the device is left on for long periods of time errors in the software can occur. Without getting too technical, this is much like a computer left to run for days on end with programs running that are not needed. Turning off the Roku can clear these errors freeing up memory to run the thing you wanted to watch.
Why it might not work? At high periods of demand your internet provider may be slower. Anything else like problems with your internet connection, problems with the NowTV servers or someone else heavily using the connection in your home at the same time will not be fixed by this. Resetting your router in the same manner unplugged for 15 minutes may help (But do not do this unless you know what you are doing).
Should I turn my Roku box off every time when not using it? Probably not, unless you don't mind waiting for the device to reboot every time before using it. Although it's not a bad idea to reset the device once or twice a month.
I hope this helps someone. Not every issue is fixed by this method but I have found my Roku boxes need resetting from time to time and all the streaming services, not just NowTV, run better afterwards. And if the problem is just with NowTV at least I can watch something else.
You know, I totally agree with your instructions because, from time to time, my Roku 3 runs out of memory and just stops, i.e. cannot react to remote control commands or anything else. So when this happened I remove the Roku's plug from it's electrical socket for 2 - 5 minutes. On replugging, the Roku reboots and all "leaked (locked away) memory" is returned to the Roku's OS.
As you have pointed out, this "leaked memory" problem is common to most, if not all, computers and computer peripherals that requires a CPU, no matter how small, memory and it's own OS to work, which nowadays is just about everything.
Mind you, sometime last year I managed to crash every CPU related item I owned and used, I had a very bad day.