POGO pads and protection against ESD events

Hi all,

I have a question regarding ESD protcetion for contact/POGO pads , and the techniques to handle ESD events properly.

Setup:
I have a 6 layer board that has 4 POGO pads, to transfer power and signals. This board has a FPGA and MCU on it.
The board is a 6 layer board, with:
1 VCC layer
1 GND layer
4 signal layers.

This board has several mounting holes that is used to secure this board to a metal fixture that is grounded.
The POGO pads are expected to be frequently accessed and touched by users, which are protected against an ESD event.
Below are the 4 pogo pads:
1. power +30VDC
2. digital ground
3 and 4 : digital signals +3.3VDC

All POGO pads except the digital ground POGO pad have ESD protection TVS diodes connected to them, with very short traces and series resistor. The TVS diodes are connected directly to the ground plane with a via.

The mounting holes are connected on the pcb in a shield/ring around the board, and this ground ring is connected to digital ground via only a 10pf capacitor.

Now the trouble I have been having is:

We have been testing by using a ESD gun to conduct direct contact ESD discharge tests, onto the POGO pads. The FPGA / MCU sometimes restarts itself. The design require that the FPGA and MCU do not reset in any event.

I am wondering if the grounding is done incorrectly? Should all the mounting holes be connected to the digital ground to facilitate the dissipation of the ESD charges? There is also requirement for this board to pass EMC.

Thank you for any advice as I am really new to EMC emissions and ESD protection topics.