Welcome to the forum @Emmaxoxo
Unfortunately this could be down to all sorts of things. Next time that it happens, it would be worth looking at the Hub to see what lights are on; that will help work out whether it is a problem with the line or with your wifi.
If the internet connection is still working then it is (probably) a wifi issue. Have a look at https://www.plus.net/help/broadband/getting-the-best-wifi-signal/ .
That said, there is a known issue with the Hub for some people. It is broadcasting on 2 frequencies. Some equipment gets confused if both frequencies have the same name. The way around this is to give each a different name. There is an explanation of how to do this in this link: https://community.plus.net/t5/My-Router/Devices-stop-working-on-5-GHz-connection-Wifi-drops/m-p/1395...
Normally this problem shows up with connections dropping rather than the symptoms that you are reporting but it may be worth trying splitting the frequencies to see if it helps. If it doesn't help, please come back here.
