Thank you for your response. I am running the 10.12.6 beta on a 2016 15 inch MBP. I had never seen this before and I had not performed an update since last Monday, so opening up my Mac today and seeing that was out of the blue.
Peculiar what makes it think there are firmware changes then... Had you connected any peripherals or similar?
It appears that this issue is pretty common among people that have the eficheck kext installed (those who have later beta versions of Sierra). So it's likely either a bug or the list of checksums, if that's what they're using, isn't exhaustive - which points to a basic flaw of this particular approach.
Peculiar what makes it think there are firmware changes then... Had you connected any peripherals or similar?
Nothing out of the ordinary. It is always plugged into my USB-C adapter for power, HDMI and USB keyboard. But when I got that notification nothing was plugged in at all.