wiznet wiz752sr-125 Stopped In Field

We have deployed a couple of wiznet wiz752sr-125 to the field as dual RS232 to ethernet adapters and we also purchased Eltima Serial Ethernet adapter licenses since WizVSP did not work with any of the computers and Windows versions we have tried.

After a couple of months of operation (with no human interaction. inside of a cabinet, doing the same thing over and over), one of the wiznet wiz752sr-125 boards has become inaccessible.

Wiznet configuration tool does not find it.
Board does not respond to ping requests.
I noticed that LD2 - Status2 green LED is turned on solid.
On other boards, LD2 (LED1) Green blinks.

No matter how many times I tried to reset or power-cycle it, it didn’t work.
Then I decide to give ISP tool a chance. I wired the board to PC USB via a 3.3V TTL USB-Serial converter.
When APP-BOOT jumper is closed, Wiznet ISP tool could connect to the board. I downloaded Boot+App firmware from GitHub and tried to flash it. It went successfully, and the board became discoverable via Wiznet configuration tool
(btw, I had to re-enter the MAC address of the board using serial terminal)

It is very annoying to see that the board firmware somehow got corrupted itself.

In addition to that we re-installed this resurrected board to field. Then we noticed that even though it appears on network and virtual serial port gets connected, it does not receive any data. We replaced the board on site, on the same PC, it worked. Currently we do not have a spare board and our operation got stopped.

Do you have any advise to check to fix this issue?

Also how do we prevent firmware to get corrupted again? Board is powered by an industrial-grade, certified power supply.