Zemkey Lost after few month of usage?

Hi

We had deployed more than 15 devices using Zymkey and Raspian latest operating system. But almost 8-10 device has been stopped working after few month usage, no idea why ?

What we did to device.

  1. Device is enclosed in box with perimeter detection using switch .
  2. Device enclosure is permeant cannot be open even by us because it is sealed with Epoxy potting resin (Black Solid).
  3. Device is in overlay fs mode in rpi so that partition doesnot get corrupt due to power cut.

How to know what causes device bricked ? Any steps ?

Naresh