iHISTORY
Back in January, after a 100 mile run at a constant 60 mph I had a sudden and complete engine stoppage. I checked fuses, FI unit and fuel pump connections found nothing and re started the bike. It ran for about a half mile before the temp gauge spun up very quickly and the fan cut in.
The day after I got it recovered home I ran the engine on tickover a few times until the fan cut in after 10 or 15 minutes from cold.
As this test seemed a bit inconclusive, and following advice received herein (thanks as always) I sourced a used HES with lead and plug and have run the bike for about 2k miles without (related) issues reoccuring.

I ordered a pair of non-OEM sensors with the intention of installing them onto my old plate as a spare.

THE ISSUE
Today I set out to do that but first ran the old set using Bert’s test (so that I would know what a successful upgrade should look like). Both sensors checked out ok at ambient temperature so I attached a thermometer to the plate by each sensor and used a heat gun to bring them up to 120c and they still both checked out ok. As an extra test I then did the same thing to the coil of mostly unsheathed cable on the back plate and again they both worked.

I am reluctant to push the temp up to the rated 160c max of the units as, although my meat thermometer is certified and calibrated, these aren’t exactly lab conditions.

So,

1) did I not run them at temp long enough to fail

2) should I do the temp test along the whole cable length and plug

From everything I read at the time the Hall sensors still sound like the probable cause but I’m tempted to just wrap the unit back up and return it to my spares pack.

Any thoughts folks, as I know you all love intermittent fault tracing?

Possibly there was a bad connection under the tank at the point where the HES assembly plugs into the harness.  The signal from the HES is low level and would be sensitive to connector corrosion.  It's possible that replacing the old HES assembly with the new one was the first time since the failure that you had wiped clean the contacts (a guess on my part here).

Thanks Rob. Back then the connectors would have been untouched, so maybe.