Check ALL your screws, dude. The ones that secure the bases to the rifle, the ones that secure the mounts to the bases if there are any, and the ones that hold the scope in the mounts.
A change of zero is to be expected when using new mounts, and that shift to the left with the boresighter seems normal. The erratic groups are from looseness somewhere, I figure.
Mine has held up for two years, and I have been pretty mean to it.
That happened when I was dumb enough to try shooting the first SC1 postal match in -34. Pretty much any condensation froze on the rifle immediately on firing. The scope had frosted over, I couldn't feel or hear the clicks anymore, and turning the knobs felt very sluggish. I thought she was done for. After it thawed, everything was back to normal and it was still waterproof. Groups were very erratic and my adjustments weren't making sense anymore. I thought I killed the scope, but it turned out to be only loose screws. The ones on the bases that you cannot see.
Those scopes are tough!