Usually this is due to a USB-connected monitor that doesn't support color transforms, so f.lux is emulating them using the GPU. If you would like to post f.lux options > driver info, we may be able to help.
If they are all DisplayLink adapters, this article should help: https://support.displaylink.com/knowledgebase/articles/1886413-how-to-enable-night-light-or-f-lux-on-displaylink