@Grpj you are not talking to Sky by posting in the forum so nobody can "investigate". However there are a number of things thst can cause you to assume the speed of your broadband is not to spec.
The most likely cause is you are measuring speeds on a device connected by a slow WiFi link to your hub. Internet speed tests record the slowest part of the transfer. WiFi speeds in your home are mainly controlled by its layout and how it is built. In many UK homes with solid internal walls speeds to drop to 25Mb/s or lower in areas away from the hub. If you buy Sky's WiFi Max package they guarantee 25Mb/s in every room. To get speeds over 500Mb/s in every room of many houses can require equpment costing several hundreds or in some cases thousands. Of pounds.
If you measure speeds using a device connected to the hub by an Ethernet cable which is capable of carrying up to 900Mb/s then you should see the true speed if nothing else is using the bandwidth. If you have a device equipped which suports WiFi6 and you are in the same room as your hub you should also see the full bandwidth. However note the service you are buying a promise of "up to 900Mb/s" with a minimum guaranteed speed of 600Mb/s.
Sky test the speed to your hub daily and you can see the results in the service checker. In very rare caes there are issues with the connection itself but full fibre very reliable. More here https://www.sky.com/help/broadband/connecting-to-my-broadband/trouble-connecting/no-connection-slow-...
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
