MacBook Pro (15-inch, 2017) MacBookPro14,3
macOS High Sierra 10.13.6 (17G65)
Karabiner-Elements version 12.1.0
When Karabiner-Elements is running the presses of F1-F12 keys + modifier arrive into application as just bare F1-F12 keys (without modifier). At the same time, other keys (not F1-F12) work as expected. If I exit Karabiner-Elements then the F1-F12 keys work as expected.
Regardless of whether Karabiner-Elements is running or not, I can see the correct sequence of keyboard events in Event Viewer (see attachment).