Fanuc robot drop/ lost program

Ideas please?
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i have a cell of 100 fanuc robots (r30ia) controller..
Randomly they will stop in the middle of a move and we have to go to the pendant & hit select/ monitor then green light go and it will continue on its course.
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also, randomly, when an operator enters the gate and then exits the cell we have to do one of two things to get the program to run again

select/ monitor + green light
or re-select the pns that it is currently in. + green light

in the plc we are getting the pns strobe just fine and we are waiting on a [do] from the robot for resume and production start.

I am 98% certain that this problem is with the robot and not the plc.. But we are all wrong at one point or another

i am aware the if another program is viewed/selected in the left side of the teach pendant and then someone green light/go's the same issue will take place, however that is not what is going on.

We have tried changing things in the configuration - no help
possibly we tried some of the wrong things???

So if someone could tell me why one would need to re-select the pns to get the robot to continue i would be very very appreciative.

Thank you all

how is the current PNS selection working? Siemens PLC's by any chance?

In my direct example when on the operator panel Manual mode is selected (Key switch) PNS 2 gets loaded ( Return @ Home ). When turning key switch in Auto PNS loads - all robot coding structure falls under this one. Bottom line is that PNS selection + PNS Strobe is a bit iffy when not done in a specific way from the PLC.

solution??

I am having this same issue on a few a few different robots on different cells. Anyone ever find a solution??