From page 10 of the datasheet:
The ESR of the output capacitor must be greater than 0.5Ω and less than 5 Ω.
The relatively large output capacitor swamps the effects of the various small decoupling capacitors which should *not* be located directly at the output of the regulator. The output capacitor should not be a film or ceramic or polymer part because the ESR will be too low.
The regulator requires a minimum load current which may be as high as 5 milliamps. Is this requirement being met? If the load current is low, like maybe while the CPU is in reset, then the output voltage will rise if the minimum load current requirement is not met.