Ancient Observer:
I had a funny experience with BT some years ago when commissioning a new radio system at Scotland Yard (long since superseded).
A central controller was installed at Scotland Yard and satellite controllers were based around London. When a radio message was initiated, the main controller figured out where the people who needed to be included were located, it would send signals to the appropriate satellite controllers and bring up the radios.
One evening we were having a lot of problems with a site in Hammersmith (about 5 miles away). Eventually, I found that the signals from the main controller were arriving at the Hammersmith controller late and were missing the window when the satellite controller was expecting them.
BT provided the data links to and from the main site so we asked them to look into the problem.
They came back (quickly) with the answer: it is down to the time it takes to go to the router and back to Hammersmith. And where is the router? Chicago! I understood the economics of it; when the local networks were very busy, it was more convenient and cost effective to route via anywhere with under utilised capacity. In the end, they agreed not to route the traffic any further than Glasgow!
And then it worked...