Help understanding 60 Hz low pass filter behavior in oscilloscope
The values in the circuit produce a natural resonance at about 89Hz based on this formula: -

Natural resonance = \$\dfrac{1}{2\pi \sqrt{R_1R_2C_1C_2}}\$

This circuit can also produce what to the uninitiated might think of as strange behaviour - it can actually resonate i.e. produce a significnatly higher amplitude at a range of frequencies just when you might have expected it to be attenuating those frequencies. This is component value dependent.

I believe this is what you are seeing. I think you are seeing this because you have one of the capacitors at the wrong value. For instance, if the 47n were in fact a 1nF capacitor the circuit would resonate at about 600 Hz with a significant peak: -



I used an online sallen-key calculator and plugged in the R and C numbers to get this. Here is the link.

I would encourage you to check the capacitor and resistor values you used.