Seatalk detection fail pattern

[opaezosu]

I was at the boat during the weekend, and for the first time I could not get the seatalk working at all: the led on the optocoupler blinking as always when the instruments are on, but this time SK did not read any of the data. I tried restarting the gpiod service several times, nothing, restarting sk also nothing. I tried manually setting the gpio hi/lo (it has worked before) to trigger the data acquisition, no luck this time. So I'm in a worse place now of what I was a week before. Cable connections did not change.

Any thoughts?