we are facing same issue in one of our robot. It's a painting robot with NX100 controller and manipulator is EPX2900.
It's a single robot without external axis.
Alarm is coming 1345 Safety circuit signal unmatched (SV) and subcode is 104.
We have changed power on Unit NTU and still alarm is coming frequently. However alarm got cleared after power recycle.
Exchange JZNC-NIF0xx interface board. We face it as a "common" error at NX100 (painting, EPX2800/EPX2050). Some relays at dual channel circuit stics and channles state is different.