If you haven't already it's worth splitting the networks (e.g. by adding -2G and -5G to the names) then you can be sure that your laptop and other devices always connect to 5Ghz and don't randomly switch to the slower 2Ghz network.
Depending on the laptop's wireless card 150Mbps may be the maximum speed it supports, even on 5Ghz. What is the make/model of the laptop?
Thanks Super Solver. Laptop is a HP Pavilion Gaming Laptop and wireless card should be fast enough - Intel(R) Dual Band Wireless-AC 3165. I have it set to only connect on 5Ghz and it has a theoretical maximum speed of 433Mbps.
I was puzzled that a reboot of the router achieved a tripling of the speeds - hopefully I don't have to do that regularly!
150Mbps is plenty fast enough (!) but not when I am paying for double that!!
The Intel(R) Dual Band Wireless-AC 3165 is a single stream Wireless AC adapter, with a max link speed of 433Mbps as you say. I would be aware that link speeds are the theoretical speed in one direction ignoring overheads. Due to the half duplex nature of wireless and overheads, actual speeds will be around 50 - 65% of the link speed. I wouldn't expect more than 220Mbps from the card.
With the card being single stream speeds can drop off quite significantly at range or if the signal level drops to something like interference.
It looks like that the wireless channel(s) you are using are becoming congested over time, downloading a wireless scanner like InSSIDer or WiFiAnalyser could help.
It is also worth checking if AC and the 80Mhz channel width is enabled in the Hub.
You upstream modulation is dropping to 32QAM which may be indicative of some noise on the upstream, but you will need to test on a gigabit enabled device wired directly to the Hub to test if it is having an affect on your speeds. You are paying for the speed delivered to the Hub, how you use it is up to you.
Thanks for the info. The router was set to AC but had Auto Channel Optimization on which limits the Channel Width to 20/40. Switching off Auto Channel Optimisation and setting width to 20/40/80 made an immediate change to the reported link speed of the connection in Windows: it was showing 200 and now is 433.
No difference to a speed test though: 139 bursting to 167.