Odd i70 malfunction?

[Hartley]

Hello!

I installed a complete new Raymarine system on my 2001 Tayana 48 the summer before last, including an e95, Evolution Autopilot w/ p70r control, AIS 650, new HD radar scanner, i70 and all the network cabling, etc. to make it work. The only things retained from the original Raymarine installation were the ST60 wind, speed and depth instruments, which I connected to the new system using an ST-to-STnG converter.

I originally installed only the one i70, but last year I sprang for another one, which I installed in the aft (master) stateroom (Something I'd always wanted - and it's wonderful!).

I have noticed an occasional problem, however, and what strikes me as VERY curious is that it happens to both i70s at the same time - every time.
It occurs only when I am in "dock mode" - with the e95 and autopilot controller turned off, though all the breakers are on. I usually have the i70s with a display showing heading plus wind speed and direction.

What happens is that I will notice that both i70 displays have lost both wind speed and direction (AWS & AWD) and that the heading section has a number showing - but it's frozen. If I attempt to turn the i70 off by pressing the power button, the initial countdown display appears ["Power Down"] with a "3" - that never decrements, so the display never shuts off. The ST60 instrument displays up on deck continue to work properly.
Cycling the DC power to the instrument buss resets everything, and all is well - for a period that can be anywhere from a couple of days to several weeks.
I have never seen it do this when we're at sea, with the e95, etc. running - only when sitting at the dock with the chartplotter and AP control turned off. I initially thought perhaps my one i70 had a glitch - but what has me really wondering is that both displays do it simultaneously!

I considered that the power system was causing the glitch - and I suppose it's possible, though nothing else seems to be affected, and the two i70s are on opposite ends of my network - one is plugged into the ST-STnG converter, while the other is connected all the way aft, at the far end of the STnG buss (where the Evo AP sensor is connected in the attached diagram). I do not believe there are any ground loops, and all the DC power wiring was installed new in 2014.

As long as it does it only at the dock, this is more of a curiosity than an actual problem - but it does have me stumped..:) Any thoughts?

Hartley
S/V Atsa