Canbus(?) error, dubious dealer explanation

Had a problem on my 2017 R9T on Tuesday where I started it but the dash illuminated as per the pic attached, and never changed. I tried switching the ignition off but it remained lit even with the key out of the barrel.
The bike did ride ok but I had no speedo, no indicators and no headlight flasher.
As I was very close to the dealer I took it in and left it with them.

I've had a call this morning blaming the accessories that I've added to the positive terminal under the tank causing a loose connection. They have removed them and the bike is fine with the fault code cleared.

Now I find this hard to believe. All the accessories I've had fitted have been there over a year with no issues. Nothing is connected via the main battery terminal, but are connected at the accessible positive bolt under the seat.
Connected were:
Pigtail for charger
TomTom mount power
Positive for led lights (fitted using relay triggered by high beam)
USB charger

It sounds to me more like it's an intermittent problem that wasn't present when they looked at it, but they've seen non-bmw wires and have a convenient scapegoat.
If I'd connected to the battery terminal directly then it might ring true, but they were fitted to the positive spur, which shouldn't affect the bike at all even if I removed the bolt entirely.anyone else had any similar experiences?

Do you believe you had low voltage because the battery connection(s) were loose?

I have at least three accessories attached to the positive terminals of my RT and other bike with no ill effects.
Typical three would be heated clothing connection, hard-wire intercom system, battery charging pig-tail.

If you want to be 110% safe in future you could buy a power distribution module (Fuzeblock, PDM60, Cansmart).