Tomorrow something will work, and the clouds will part, and the sky will be blue .... for about an hour.
Some people are just plain cursed, that's how life is, I'm not alone. Enough philosophy, so
What is the servo being used?
What is the power supply for the servo?
How long are the wires from the servo supply?
I would think things would work worse when using the same power source for both servo and Arduino,
so ???
Running the Arduino off the power in the USB cable may be a problem with servo systems, I rarely do it.
For my part, I "always" use extra electrolytic [eg, 220 uF] and bypass [0.1 uF] caps on the servo power
distribution point, to help filter servo motor noise.