I have this spring along with the the TWM shifter their BigR shift knob (+500g). I just went and checked because you had me thinking... I have the same pressure and snap back into N moving left or right. I love this combo FWIW.
Very strange issue, you should put the original spring in and very the issue is not with the shifter.
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2016 Sport 6sp Deep Blue Pearl || AAM intake || FI TDX non-res CF + HF-Cats || TEIN MonoSport w/EFDC-II || Hotchkis sways || Z1 34 row oil + ps cooler + diff cover + oil pan spacer || TWM Short Shifter || SPL everything || MA-MS diff cooler || Stillen brake duct || ++
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