Looking at the forum it seems this is a common occurrence, and rather than hijack someone else's thread, I'd thought I'd start my own.
I'm a Plusnet customer, and have chosen to use a BT Smart Hub v6 that I purchased (brand new and unused) privately. I configured it to work with Plusnet (as I did with my Hub 4, and also my Hub 5).
However my Smart Hub has been frequently dropping the connection, for no apparent reason, whereas my previous Hubs were rock solid in their performance. Nothing has changed with my line , sockets etc (and being and ex Openreach engineer) I'm confident the external network is fine.
I've posted some screenshots of my connection speed, SNR etc ...
InInterestingly I note that the firmware was updated on Jan 12th, and my connection has been stable now for 4 days (which is the best it's ever been with the Smart Hub.
It would be nice to see a change log for the recent firmware updates 😉
The BT Smart hub is just a BT Branded product, just like a BT phone, so there is no reason for them to refer you back to a BT Retail forum.
I would suggest that you simply return the Smart Hub, as being unsuitable, and just use whatever Plusnet have provided, or buy your own third party router.
maybe the latest firmware update has solved your problem as you now have 4+ days stable
BT do not publish a change log for firmware update