If you don't find the answer with a little bit more work... It should be possible to make a few changes to the Marlin firmware and have it update its status all the time. I don't know what you have available but even a few LED's that can be turned on and off at different times in the code would be valuable. If the firmware is shutting things down because something is too hot, that won't be hard to isolate and report in the firmware. Or if the firmware has run out of GCode commands to do and is sitting there waiting for instructions that won't be too hard to report either.