Modification Galaxy Note 20 Ultra Motherboard did not go as planned.

I had 2 Galaxy Note 20 Ultra Motherboard that is in Normal Condition. One is the Hong Kong Version and the other one is the Japanese Version.

I bringed both motherboard to a repair shop to do a Sandwich Board Seperation, because I want to swap the top sandwich board to modify the Hong Kong version of the motherboard to have the 5GmmWave Antenna.

After the Sandwich Board Seperation is finished, the Hong Kong Version of the motherboard is able to power on but it restarts every minute. The other motherboard the Japanese Version is able to power on normally, but it shows an Unknown IMEI and Baseband do the repair shop decided to redo the Sandwich Board Seperation.

After few times redo the Sandwich Board Seperation, both motherboards are completely died. Can you tell me what caused the motherboard to completely died?