I've seen on this forum that occasionally the mag box and bottom metal may have been installed incorrectly. Additionally your torque on action screws sounds off.
You might try removing bottom metal, remove the mag box metal and leave it out for test.
If your stock has pillars, torque front and rear to magpul specs or go up to 50-65 in lbs. while at your shooting place. See what it does. The magpul stock may have issues binding in the area of the trigger, mag box area, barrel channel, screw holes.
Your groups seem to be jumping left to right. You might want to check velocity over a chronograph "just because". Sometimes you will find a wild shot can be tied to velocity.
Mis-assembled mag boxes happen. There has to be verticle play in the mag box when installed. Non factory stocks can be off dimensionally or there could be a piece of plastic burr in the mag well binding the assembly.
Take it one thing at a time and bring your tools to the range. Patience....