But then about 5 days ago after the 2 week regular BT Hub reboot
None of the BT Smart Hub 2's I manage for friends/family reboot every 2 weeks.
It's always been something that only happens on some users BT Hubs, but even less on the Smart Hub 2.
I think it would be much easier if you stuck to Mbps when discussing your throughput rather than jumping back and forward between Mb and MB.
How are you testing speeds? You don't say if it's wired or wireless?
If you are seeing any slow down in throughput you should use the Speed tester built in to the BT Smart Hub 2.
It tests the speed to the Hub only, not to your PC/laptop/phone, meaning it rules out all the users hardware.
It's something BT will ask for you to do before looking in to any speed complaints anyway.
If the Hubs built in speed tester shows slow throughput then there's pretty much nothing you can do and it needs passed on to BT support to look in to.