Good day, I'm having the same issues. I thought it was my Motorola g7 power causing extreme slowness - <5mbps DL speed on the bt smart hub 2. But we went away and saw I was able to get normal WiFi speeds on the router on holiday. So it must be the router. Sounds very similar to this post. Please could you assist BT? Might be the smart hub 2 as well?
THis started happening in June this year 2021. The hub was fine until then
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