Shunt Current measurement noise
Your circuit there is very dangerous and will not work correctly.

You are applying 240V to R6 and R22 which will cause the input of the amplifier to go way outside its common mode range.

How are you connecting the scope to the circuit? Generally scopes are grounded to the AC ground so the ground clip on the probe will be connected to the AC ground.  That is not the same as neutral and will have noise on it relative to neutral.

You say you are using a "non-isolated" supply.  Why?

The better way to do the current sensing is to use a current transformer - this will be safer and provide isolation.

Current transformers might have a primary with just one turn and a secondary with 1000 turns - this will give a ratio of 1:1000.  So 1 Amp in the primary results in 1mA in the secondary - if you then put a 1 Kilohm resistor on the secondary (usually referred to a as burden resistor) it will give 1V output for 1Amp in the primary.