I upgraded to Gig1 with a hub 4 and instantly had problems. Had an engineer appointment and was told the Hub 4 is not fit for purpose with Gig1 and that a Hub 5 would be requested.
When I chased the request, I was basically told no Hub 5 would be ordered as there are no issues with Hub 5 and Gig1.
Fast forward six months and was still having issues, even using a third party mesh system, I contacted Virgin who ordered me a Hub 5 with no questions.
Have been using the Hub 5 now for 5-6 months (with no third party mesh system) and have not had one single issue.