nRF52840 power-on reset failure

[JordanYates]

Under the recommended operating conditions (page 611) in the nRF52840 datasheet, there is a note specifying:

Important: The on-chip power-on reset circuitry may not function properly for rise times longer
than the specified maximum.

Given a device (with SWD access), is there any way to detect whether the POR circuitry has failed?

Is the error condition when this occurs the same as was stated for the nRF52832 here? (stay in reset state with no code running) 
https://devzone.nordicsemi.com/f/nordic-q-a/47531/power-on-reset-on-nrf52832

We have several devices that we suspect to be in this mode, but wish to validate.
The behavior we can observe is:

• The standard software is not running (it contains a watchdog)
• SoC is being supplied 3.3V
• Pin 18 is configured as nRESET (implying an internal pull-up resistor), but the nRESET pin is low
• Physically pulling nRESET high does not result in code executing
• We are unable to connect to the device using JLinkExe tools
• Physically disconnecting the battery and reinserting it resolves the issue (code starts executing)

[Simonr]

Hi

Please check out this case, where my colleague Jimmy has provided some information as to how you can store the error code in your Flash memory and print out the reset reason (NRF_POWER->RESETREAS) after the system powers up.

Best regards,

Simon

[JordanYates]

Hi Simon.

I believe the RESETREAS register will be of limited use as the only way we have currently found to recover these devices is to remove power from them. The problem is that the system doesn't power up, despite the voltage being sufficient. On devices that do recover from being flat (i.e not the problem I am trying to resolve), the RESETREAS register is typically 0x00, as would be expected.

Cheers,
Jordan