We've just upgraded to fibre x max and since that, speeds are only temporarily what they should be and all devices in the house lose connection to router at regular intervals. We've also got problems with the tv box we were sent and get a pink screen whenever we turn it on.
We've had similar issues on since April when we upgraded to Fibre X Max and vodafone tv as well. Although our speeds are ok, the connection drops out for up to a minute or two. The VF TV freezes when the internet drops out, but doesn't do the pink screen thing.
My suggestion would be to steel yourself for the pain that is to come when trying to get it fixed and the amount of nonsense you have to go through with call wait times, false "I will surely fix this for you" comments etc. It's been very frustrating for us. If they don't fix it for us in the next week, I may consider changing ISP. To be fair I did miss a few call backs as I didn't feel like repeating myself on the phone and also had other things to do at the time.
If they haven't fixed your issue already, good luck. And apologies that I wasn't really helpful much like many of the poor helpdesk staff I've spoken to who's hands are tied sometimes because they need to wait for the mysterious 'Tier 2' team to do something.