The second-order Sallen and Key lowpass filter has a certain amount of max gain to be a Butterworth filter. If the gain is too high then it oscillates.
I make this type of filters using a gain of 1 for the opamp, same value resistors and the capacitor values are 2:1, or use the same value capacitors and a fgain of 1.6.
You can use the Texas Instruments Filter-Pro program to calculate lowpass filters with any amount of gain but the capacitors and resistors have odd values.