@Danjones101 a Virgin Hub by any chance? Worth enabling the guest wifi option on it and trying to connect the NowTV box to that access point instead.
Unfortunately @Danjones101 you appear to have tried all the other known solutions.
The only other thing might be to turn off the 5GHz setting on the router, but the guest wifi trick is normally 2.4GHz only anyway.
Apologies if you've already tried this & I've missed it from the thread. If you haven't, it may be worth doing a factory reset & check for software updates, both can be done from within Settings on the NOW TV box.