ASRock Z170 Extreme 4 with BIOS version 2.30 was motherboard #1Gigabyte GA-Z170XP-SLI with BIOS version F5 was motherboard #2
As I initially reported, both were reporting the error involving f0:1f.0
Not surprisingly, there are no f0:xx.y devices. The closest I suppose is:00:1f.0 ISA Bridge: Intel Corporation Sunrise Point-H LPC Controller (rev 31)
At the moment, I am back on vanilla 4.6.0, and no such error messages are being reported via 'xl dmesg'. I am guessing reporting of this error was added post-4.6.
Eric