I believe that means you have too many jobs. Once you increase the amounts of residents to fill jobs that *should* go away. Check your Population Detail screen to see if your available jobs is high for that wealth level.
Makes sense- if there are too many jobs available in any particular wealth-level, the productivity requirements for each worker goes up in the jobs they occupy. Every plopable and zone-generated building requires x amount of man hours to operate, so if there are 4 jobs that need to be filled and only 1 Sim to do those 4 jobs, they become overworked trying to keep that building active.
