Self-destruction as in: Self. Destruction.
The “hack” that was implemented (see topic) wasn’t the cause, it was the fact the device lacks any means to fail gracefully in the event of overcurrent and/or excessive heating.
The truth is these cheap, self-certified devices are probably fine for switching on LED lighting but are woefully underdesigned for handing high-current loads. Nevertheless, that’s how many people use them and then rationalize it by quoting the device’s specifications (which amounts to relying on materials-failure as opposed to a proactive, graceful shutdown).
EDIT
Google ‘burned sonoff’ and check the images. They don’t all fail as catastrophically as in the image above; other examples involve the localized failure (re: thermal destruction) of traces and/or individual components. Basically, in lieu of any self-protection it relies on its components to also serve as fuses.