...I sort of knew what I was letting myself in for with going with a "budget" / "prosumer" minded company with all the skimming on the components and build quality to keep prices down...
I have neither affiliation with, nor any particular loyalty to, Line 6 or any other manufacturer or supplier, spuddle.
Indeed, I reserve the right to always "call it as I see it".
So when I say that this sort of quality control issue with early issues of equipment is far from being exclusive to Line 6, you know that my comment really does stem from my experience, not from a "paid piper playing his master's tune".
It's also been my experience that's led to me forming the opinion that the very existence of this type of forum, coupled with the usual high quality of their equipment, (once "de-bugged") puts Line 6 into the very top echelon of audio manufacturers, ...particularly in terms of "value for money".
...None of which in any way excuses or diminishes the problems you've faced.
I'm just hoping to offer you a little "hope" !