How to determine which setWatch callback function triggers the E.getErrorFlags() CALLBACK error

Mon 2020.03.30

A new flag has appeared, 'CALLBACK'

[
  "CALLBACK",
  "LOW_MEMORY",
  "MEMORY"
 ]

https://www.espruino.com/Reference#l_E_g­etErrorFlags

'CALLBACK': A callback (setWatch, setInterval, on('data',...)) caused an error and so was removed

When I attempt to view memory free at this point, I'm faced with another issue,

=undefined
>process.memory()
Execution Interrupted
> 

Instead of reporting back, the WebIDE is locked up at this point. I've viewed WebIDE :: Settings >> Console and am able to verify that the keypresses aren't being sent through, which makes sense as they don't show in the console either.

I also note that the low level peripherals still output pulses, so am unable to control the device at this point. I made mention of the suggestion/ability to reset these in post #12 three weeks ago:

post #9 - #12 Tutorial example output anomaly using low level access PPI on MDBT42Q breakout board

Disconnecting the WebIDE and then powering down the device are the only ways I've discovered to get back access.

There doesn't appear to be many forum responses for the CALLBACK flag with E.getErrorFlags()

What methods may be employed to determine which callback causes the error flag to be set?