I think it was a few years back now, I started having all manner of problems with shielding whilst tig welding after doing a bit of workshop rearranging. I was trying to weld aluminium at the time, and no matter what I did everything including the tungsten would oxidise immediately. I checked the argon flow, checked for leaks made sure I had pre-flow, post flow. Cleaned everything meticulously with acetone, etc. etc. Nothing worked.
It was quite a bit later after a couple of beers that I worked out that the new position for my welder was directing the cooling fan directly across my welding area, blowing away my argon. Being a good little vegemite with long sleeves and gloves, I just didn't feel the breeze.

Anyway, years later, but none the wiser I fell for it again after some equipment rearrangement, only took me about 10 minutes of trouble shooting this time, but still plenty of swearing and a good forehead slap to finish off with.