I’d forgotten to update this topic and tell you that I’d found the cause of the problem.
In fact I thought that the electrical power coming out of the Z2’s two USB ports was sufficient to power both Lc6000s at the same time without adding an extra mains adapter.
And that’s clearly not the case. Without at least one additional mains adapter connected to one of the LC6000s, at least one of them will have capacitive plate malfunctions at times. Leading to poor detection which reminded me of an earthing problem.
As the Z2 has its own power supply, I thought it would work like a USB hub with an external power supply, but that’s not the case.
By adding an external power supply to an LC6000, I no longer have any problems. To be on the safe side, I’ve even decided to use a power supply for each LC6000.
So the problem is solved.