They are looking at visual representations and / or signal level readings that indicate something out of spec. Green good red bad. Your issue is a series of technicians that have not found your problem (admittedly many intermittent issues are a pain in the ass to find) Here is an example of one of the parameters they can look at all the traces in the green are in spec and you can individually identify a modem that is reporting out of spec levels. The problem is they are not finding the root source causing your issue.
These are traces from 71 individual modems and it is fairly easy to tell which modems have issues either bad equipment of bad signal paths to and from the device. Not as easy to find actual cause.
