Thanks for the update and the excellent pictures showing the linear indication. I have the same rack but have removed it to make way for my Happy trail panners. I will rememebr the issue you had with advmoto next time I shop for my strom. I have had some issues there as well, but nothing like yours.
Thats is a strange place for fatigue cracks. If the givi was loaded, I would tend to think the indications would be on the leading edge of the plate around the pins. Not on both sides. Perhaps it occured during the removal and reinstall of the 46. Not during the riding process. For this to crack here, the pins would need to be lifted from the back judging on my experience in metal fatigue cracking.
"Pain is weakness leaving the body"
"Nothings possible until its done!"
"If ya can't afford the fine, take the lead!"