ESP32 waking from deep sleep into firmware upload mode

[iParcelBox]

Hi,

I've got a few devices which occasionally wake up from a deep sleep timer into firmware update mode, then because they are running on battery, get stuck until power is manually removed. We have nothing connected to GPIO0 when this happens (although the pin is exposed to a connector).

Before going into deep sleep, do I need to be manually setting the internal pull-up on GPIO 0, or is this a hardware issue of some sort due to EMC or similar?