Blue light filter turns on automatically at sunset, but often doesn't turn off at sunrise
It turns out that it seems to be related to the power-saving features on the S7. Apparently at some point, the background process that automatically turns the filter on and off at scheduled times got added to the list of processes to be managed by the power-saving mechanism, after which point, any time my phone was in power-saving mode and had not been used recently, the scheduled toggle of the filter's state would not fire. I'm assuming that was just never the case at sunset, as I'm much more likely to have used my phone recently at sunset than at sunrise.