Powering an Uno, that draws about 50mA without anything else connected to it, through an RC filter with a 47ohm resistor doesn't seem right.
That could have a volt-drop across the resistor of 0.05A * 47ohm = 2.35volt,
leaving only 2.65volt for the Uno.
Maybe better to replace the resistor with a (1N5819) Schottky diode.
100uF is also a bit small for brown-out spikes (the Uno already has 47uF).
You could increase that to 470 or 1000uF.
Leo..