Fibre broadband stable for along time but recently connection is extremely unstable.

Changed over to Fibre broadband some time ago and over several months speed improved to around and a stable average of 22.5 Mbp/s. However, my broadband connection has recently become more and more unstable and is now unriable and extremely unstable as you will see from the attached PDF of results from Ookla.

When I log into the H633 system information seems to indicate a a reasonable connection speed even when the Ookla speed tests indicate otherwise. However at any moment the actual performance flags to well below acceptable levels and there seem to be intermittant latency as when I listen to streaming services like internet raio the sound drops out on regular intervals and then reappears after a few seconds - totally ruining the listening experience. I have tested the router connection both via ethernet and wifi but the problem is exactly the same even taking an ehternet feed directly from the back of the router. I have attached the H633 System Info below. 

Can some one please look into this as this situation is now intolerable and whereas I can restore/reboot the service back up to a download speed of around 22.5 Mbp/s no end of rebooting the router seems to cure the problem for any length of time.