Flickering 230VAC Halogen dimmer
R2 may have too high of a value, and reversing the parts order only proves something was wrong. The sidac may be damaged if the potentiometer went to zero ohms in your original design, which is the one you should be using.

Right now that capacitor is putting 20 mA into the gate of the triac, through the sidac. Way too much current.

That 2 K resistor is in series with the potentiometer to prevent a 'zero ohm' condition. Put it back the way it was and try another sidac. If it is a sensitive triac make R2 3.3 K. If it needs more drive current drop the potentiometer to 250 K. These circuits are too simple not to work unless something fails or is a miss-match.