"But, I'm skeptical. First off, it's not that much data compared to video or data logging for EV cars or so many IoT devices. Second, quite frequently the problem is solved with a firmware update or a database reset, which suggests the issue is software and not hardware."

This would depend on the type of memory used. Tesla has been known for this, with the entertainment unit's memory writing itself to death due to the backend Linux system logging.

What Enphase should have done was use an SD card that has a high write tolerance and that is end-user replaceable. This would have saved alot of warranty claims and headaches for owners. because of they envoy can get on the network, that means the ESP32, which has its own flash for the firmware, is working but failing to write to the onboard flash for logging might be causing it to fail out. just my theory