Hello,
I had issues with FN keys on HP ProBook 645 G1 using unstable suite.
Three FN key combinations (brightness +/- and microphone toggle) were
not recognized by XFCE or X at all. To fix this I created custom .hwdb
file for eudev, then issued command udevadm hwdb update and key
combinations started to work immediately. I attach my custom file, I
hope it might be useful for someone.

Best regards,
Tomasz Jeruzalski