Welcome to the forum. It's not a good idea to have the router right next to the device you are streaming to, I suggest you place it at least a couple of metres apart. Try rebooting the broadband router to make sure it's on the best wireless channel, and try a forced software update on the NOW TV box to see if it helps.
Press Home on the remote to take you to the home screen. Then do the following sequence on your remote quickly and smoothly
Home (x5) FF (x3) REW (x2)
If done correctly a Secret Screen will appear (if it doesn't, press Home to go back to the start and then try again). Choose Update software and allow it to run (even if it reports the same version as you already have).
If it doesn't I'd suggest popping onto live chat to see if they can help further, although the white NOW TV box is getting pretty old now and apps do run slowly on them, at some point if you want to continue with NOW TV I'd suggest upgrading to the new NOW TV stick.
You can get to live chat from the Contact Us page
(expand the Anything Else section at the bottom for options)
If its a Now TV stick, then you may get a better answer in the Now TV stick sub forum https://community.nowtv.com/t5/NOW-TV-Stick/bd-p/NTVStick as this is is for Roku devices, which will either be the purple stick, or the Stick+