capacitor sensor circuit
Sounds like you forgot to mention some important circuit details, e.g. a feedback from the comparator output to the switch control?
However, if you get 60 to 300 Hz depending on the capacitance and the measurement is reproducable, the circuit seems to operate perfectly. If so, what's the problem?
P.S.: If you get chaotical frequencies with constant capacitance, it would be meaningful to reveal the operation pricinciple of the control circuit and to present considerations, why a stable operation should be expected at all.