I'm copying and enlarging upon the following Original Post of mine from the General Discussion section to this one which I can see is more appropriate:
My service is with Zen Internet and the package is Unlimited Zen Fibre 1 .
I've been happy for several years with consistent download speeds in excess of 30Mb/s.
For more than a week now I've been getting a much reduced service in the evenings, typically between 20:00 and 23:00 during which time video streaming is not possible.. The service returns to normal each morning.
I set up a monitoring configuration with the router connected into the Master test socket and just a single device connected - a Windows 10 PC with the Task Manager showing nothing running except my speedchecker.
Running the Zen speedchecker at any time during the day shows a DL speed of 30Mb/s or more.
Running the speedchecker at any time between 20:00 and 23:00 shows a combined DL speed of 7Mb/s with a tbbx1 (single thread) of just 1.3 Mb/s which is what prevents me from receiving video streams.
A tbbx1 reading this far below the combined/multithread reading can really indicate only one thing - contention on the Zen network. (Any alternative thoughts on what might be the cause of the problem would be welcome.)
My real problem is that Zen support is unable or unwilling to confirm that this is what's happening. Their response is that "they're looking into what might be the problem".
I'm happy to ride with a supplier I've had a good service and good support from if they admit/confirm there's a problem, that they're sorry and that they WILL find a solution. What I can't deal with is evasion, particularly if it's taken me hours to provide the test results I've been asked for and to still need to research the problem myself.