Is this FTTP ?, obviously BT are unlikely to supply every address affected, so Sky , Talk Talk or whoever customers will need to report faults to their own ISP ,
If the problem is on a common part of the Openreach network , probably at the headend as everything else toward the customers is passive, then either ORs own monitoring systems will pick up errors/congestion or whatever , or failing that , Openreach field engineers would have to pass their fault reports back for further investigation, rather than closing the faults as ‘ right when tested ‘ , ( if the things the field engineers can check on the passive part of the FTTP network are OK ) , but this is just as likely to be done using a Sky fault report as a BT fault report, if OR get multiple reports on a single ‘PON’ from various ISP , then they are more likely to accept that there is an issue on a common part of the FTTP network and investigate it.
Obviously you can no more expect BT to take responsibility for Sky customer’s problems as Sky would do for BT customers , Openreach is no more accountable to BT than Sky , or any other ISP that uses OR products, if the OR engineer that visits you states they can find nothing wrong , you could ask that they pass the fault for SFIO ( special fault investigation ) to look at , as you are experiencing poor performance even if it isn’t present when the engineer is present.
