Hi @Mm91 and welcome to the forum. The Wi-Fi checker is not very useful in my opinion and at bestjust gives an indication.
One of the main reasons for buffering or freezing is the quality and speed of the Wi-Fi signal being received at the TV/puck and not that being received at the router. This can be checked with the Netflix App (Get help > Check network) and is often much less than you might expect. The minimum speeds recommended by Sky are as follows:
HD = 25mbps
UHD = 30mbps
HD + 1 puck = 30mbps
UHD + 1 puck = 35mbps
These speeds assume there is nothing else in your home using up your WiFi bandwidth.
If your speed at the TV is borderline try connecting via Ethernet cable. If this is not practical you can use powerline adapters (about £40 at Amazon). Note the Ethernet port on the Glass TV (& pucks) only supports 100mbps so don't waste money on the more expensive 1gb powerline adapters
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