As Langers said before you need to look at a wiring diagram and follow the power supply to unresponsive modules from the battery to the fuses / relays into the controllers.

 

There will be one or more that do not have power or ground supply.

 

A good auto electrician should be able to do this too.

That is the correct way to find it but the OP has 7 controllers that won't communicate and many of them are in horrible places for testing.  I reckon it will be more than a single controller, more like a big broken wire somewhere so a good inspection of the loom is good basic start.  Easy to say from an armchair I know! 

Either way would be good as a restart of furtherance but not everyone has the facilities (in many senses) to do so and of course it would appear that possibly again those in or associated to the motor trade haven't perhaps been as successful as one would hope in their endeavours, to keep it polite.  Pity there aren't more people doing a decent job (and attitude to their work and customers) in the motor trade, whether it's worse or better now than at other points in time is too difficult to tell, but it can be even more wearing on those that are not fully well health wise and have to rely on them.