It is "normal" problem of needle valve. There is so little tolerance between the tapered needle and the orifice that even small movement of the needle will make a big difference in the flow.
Before you commited to my statement above, make sure it is not the reactor's flow problem. Check and make sure the reactor media is not compacted, and all the tubing is not blocked/clogged.
If everything else is in good shape, see if you can take the needle valve apart (I am not familiar with your model, so I don't know if this can be done at all...) Make sure the needle is smoothly tapered, and there is no salt deposit or corrosion on it (it does get corroded if you are not careful about back pressure from reactor when you take the regulator off the CO2 cylinder) Check the orifice and see if you find any rust/irregularity (very hard to see in mind...) Make sure the needle assembly's thread is not stripped, and there is no lateral movement when you shake (be gentle, a needle valve is very delicate). Sometimes if you over-tighten your needle valve, and push the needle too far in, you can damage the needle's shape, and ruin its tuning ability.