Hi,
ESD? No. This is electrostatic discharge.
EMC. Electromagnetic compatibility.
A metal case should be considered as a faraday cage. Where the whole case should have the same voltage at any place.
I'd use a common shielding_GND (on the PCB)!for all connectors. With one RC to the system_GND.
But I see no problem with your circuit for now, since the C should act as short circuit for HF.
There rather is another problem.
* other connections to the GND or case, like a GND loop via earth_GND.
* or HF noise introduced by an external device (like an SMPS)
* maybe a soldering fault or PCB fault that generates a short circuit between USB_shield and USB_+5V .... or something similar.
* maybe you don't have a solid GND plane on your PCB ... causing a loop via GND traces on your PCB.
Klaus
Btw: Yes, the different GND symbols are confusing.
* if they refer to the same signal, then use the same symbol.
* if they don't refer to the same signal, then give information where the belong to / how they are used.