I have a feeling that your device is connecting on the 2.4G band, rather than 5G.
The HUB 3, by default, has one SSID (Network Name) that controls both bands and it dictates what the device should be connected on.
You can, however, split the two bands into different SSIDs, by accessing your HUB on http://192.168.0.1 ,and you decide which band to connect to (You can just append the existing names with '_2G' and '_5G' as I have done on mine):
Once you 'Apply Changes' at the bottom the connection will be lost and you must connect your device, hopefully, to the '********_5G' SSID.
All other wireless devices will need re-connecting, since the SSID has changed!
Yeah i have done this already, it has been fine up until now
Ah, you didn't mention it hence why I did!
Could you access your router using http://192.168.0.1/ or http://192.168.100.1 for modem mode . Don't log in, select the 'Check Router Status' option and paste your 'Downstream', 'Upstream', and 'Network Log' tabs?
At least we can check the stats to rule out an issue with the line.