I was watching Netflix through BT last night and exactly the same issue, almost unwatchable.
Have you tried using a PC or laptop instead of the BT box?
I'm also on FF500 and I've had no problems with buffering on my laptop or smart TV but I can't comment on the performance of my BT Pro box because I have no need for it and never use it.
I don't believe it to be a server issue, you could try using a laptop or PC and if that works OK then you know it can only be your box, in which case you could try a factory reset
Thank you for posting this, it's almost like I wrote this myself. I have exactly the same setup, Cat 6 cables and one switch between my Fibre broadband and TV.
I'm new to NowTV and the buffering/stuttering issues are the worst I've experienced of any app so far.
It's not just Now TV for me its any of the apps using the BT Box. I have freezing/buffering issues on Now TV, ITV X, Netflix, Prime. Basically anything that isn't BT. they play fine through the smart TV so it's not the download speed it's the interface through the BT Box.
If you haven't already, try a factory reset, note that this entails more than just switching the box off and on.
yeah I get that as well sometimes and when I open up NOWTV it always takes a while to open up the home menu screen and also the shows to become HD but I think thats just because Im stuck on 60mb and it would be better when ever FTTP comes..
Already done that, all that happened is that I had to re-hide the channels I didn't want to see. The lag/non start still happens but only on the BT box, not on any other system.
I have FTTP 500mb makes no difference 🤷
@StuB71 I watched Jurassic World: Dominion yesterday and had a couple of spots where it buffered or the quality dropped from 1080p to what looked like VHS 🤣. It really is poor that NowTV struggles to deliver a constant stream when everyone else had no issue in pumping out 4K HDR with Atmos over 20-ish mbps... My connection varies between 80mbps and 110mbps and NowTV is the only On-demand service that stutters so, it's definitely a NowTV issue despite them saying otherwise. This buffering happens regardless whether I use Roku or BT TV Youview...
You have to wonder if there is any connection with Sky moving everything over to Comcast's global technology platform and performance issues on NOW, Glass and Stream?
The latter two have also been filling social media and support forums with similar reports of picture issues.
Teething problems? Lack of capacity? Lack of technical competence? Who knows.
I would be annoyed if I was paying for NOW and this happened, if I was paying for the supposedly premium offering of Glass or Stream, I would be fuming!