Diagnosing communication problems between modules

We had two cars this month with several modules suddenly going offline, and the usual scan showed a long list of communication faults without making it clear where the actual problem started. I want to improve our setup for diagnosing CAN and other network issues instead of spending hours checking wiring almost blindly. I’ve been looking at the diagnostic equipment on ECUTools and there are several tools that seem suitable for this type of work https://ecutools.eu/ What equipment do you find most useful when multiple modules stop communicating or you suspect a network fault?

For this kind of problem I’d definitely want access to the network lines through a breakout box and a scope to see what is actually happening on the bus. A scanner can tell you which modules disappeared, but it won’t always tell you why. Once you can check the signal and isolate different sections of the network, finding a bad module, wiring fault or short becomes much more systematic.