Sometimes I have the same issue, but I use the official rom. After one or two reboot the issued is solved.
Only one time I turned on the torch with ToolBox and the issued is solved.
I have google camera so I thought this the cause, but you do not have gapps.
I never opened an issue because is not easy to understand the cause.
In about 6 months I've been using LOS, it happened about 5 times.