either out of battery or over pressure load is my guess
55 gr is close to max with 55gr, but not a compressed load, could you maybe have gotten an overcharge by accident?
would a loose barrel nut cause this type of OP issue?
other thing I might be wary of is case head separation?
mistake of pistol powder? (probably not)
I would pull all the rest of those loads to see if you can find an issue, and look for signs of case head separation on the fired brass, varget powder is pretty easy to tell apart from others as it has a goldish tint to it--I can still read the brass manu in your 2nd pic
savage axis 2? check out this article :
https://www.thefirearmblog.com/blog/2016/10/24/man-insane-battery-firing-savage-axis-can-happen/