Robot stop picking [PickMaster 3]

Hi,

We have a line with 2 robots in line using 2 vision pick work areas and on place work area.
For the 1 vision pick work area we use LB & ATC combined, for the second work area we use only ATC.
Sometimes during production the second robot stop picking from the first vision pick work area without reason but he is still picking from the second pick work area.
The only way to solve the problem is to stop and start the robot (it is not needed to stop the project). The rebalance strategy is “rebalance among running work areas”

What could be the reason?

BR,
Fabrice