It might be your gas is a bad batch, had one bottle last week and couldnt weld alluminium with it at all, usuly i have no problem repairing engine alloy sumps, lorry diesel tanks and AC pipes when the gas is good!
Gas problems could be down to the regulator you are using.Single stage will not work as the bottle empties.If you are using a single stage regulator you will find that,as the bottle empties,the diapram loosens off due to the the lack of pressure.This could be a problem.The weld looks good ,go for a multi stage regulatorHave seen this a couple of times in 40 odd years of welding
We were always told to leave at least 1bar in the bottle , lots of people run the bottle to zero and even take the gauge off with the valve open a perfect way to contaminate the bottle . I imagine the bottle would now have to be brought down to a vacuum before filling but is it done ?