50 Mbps sounds like wifi is connecting over 2.4 GHz. Check the name that your hub is using for the 5 GHz signal, because due to a fault with the firmware, the hub can randomly rename its 5 GHz band, which for your devices mean they lose all access to that channel because they don't recognise the new name, even though a 5 GHz signal is still being broadcast. Also, when you're in settings, change the 5 GHz "channel width" to 20/40/80, as that helps get much closer to your contracted speed. Even if you reset the name, there's no guarantee it won't lose your setting again.
A better approach still is to accept that the hub is provided for free, and represents the quality of anything given away for no money. If you do accept that, then your best option is to consider what many of the rest of us have done and buy your own router or mesh wifi system, which will cost from £40 for a competent entry level router to £100 for a competent entry level mesh. Some people balk at the idea of paying money for their own wifi gear, arguing that the hub should work reliably for all their needs. That's fair enough, but then it's a case of taking the hub as it is without complaint, warts and all (and there are many warts).
