Do you have a beta group?
As a developer I have been using Sierra and we are "not quite" compatible.
@Collyde Which version of f.lux and Sierra are you having trouble with, and what's the trouble like?
f.lux 37.7 & macOS 10.12 (16A323).
Biggest issue is that it does not recognize, 10.12 has a dark mode. For me, the biggest bother.
I have seen an instance, where it could not get the correct time or location and would not darken.
I still use it.