superhub 5 slow at downloading mail on wifi

I have noticed that anytime i hit mail on my iphone in safari  it sits in downloading and checking for email for ages   . I then flick it to mobile data and they all come in quickly. 

so so far i have checked iphone all up to date , changed the ipv4 from automatic to boot then back to automatic ( mentioned by someone )

reset the hub , removed all cables.    my download is 750 and upload 100 so no issue 

I never experienced the issue with the hub4 that i cancelled few weeks back and i recontracred as was cheaper

Doing  a wee google search seems to be a recurring issue.       virgin are sending someone out but can’t see changing box will work defo a hub5 issue