This error appears right after a job configuration or when trying to start the job run.
It indicates the job misconfiguration: the Agent is added to two different job. In one of the jobs it's configured to sync a folder with Selective Sync enabled, while in the other - its parenting or child folder with Selective Sync disabled.
The only fix for it is to either enable or disable Selective Sync for both jobs. The best way to see them is to go To AGENTA tab -> Agent -> Job and review its jobs.