When I changed to Plasma for a DE, it didn't occur to me to get rid of Redshift, which I'd been using with Budgie. I did turn on the Nightlight setting (in the System Settings/Displays category), and that seemed to cause conflicts.
With two different things controlling brightness, it appeared to me that one would make the change, and the other would soon notice and change it back. They didn't seem to be making their changes at exactly the same time.
Every morning and evening there came a time when our screens would slowly flash back and forth between day and night screen brightness for a while. So on these machines (all Plasma now) I uninstalled Redshift (and rebooted), and now there's no more flashing.
