Yes, it may be a problem in unstable mains voltage cases (like me too). I removed the R223 and use a low-drop 3-pin regulator, installed on a decent heatsink (I used NJR NJM2396F63 which is actually 4-pin, but actually 2 pins of them tied together; but it can be anything supporting suitable current) instead of it. If you are not easy to modify the circuit - the only way to do this is to use an AC mains voltage stabiliser (or UPS maybe).