I bought a used VLP stock a few years ago that was cracked like that as well. From the rear pillar to the mag well. I feel it was from someone over tightening the action screws on the stock with pressed in pillars that were slightly lower than the action inletting.
I actually took mine to my gunsmith, and in addition to basically gluing the stock back together, he milled a couple slots across the split area about an inch wide and the depth of the mag well, and filled the slots with bedding material when he bedded the action to help strengthen that area. Also had real pillars installed as well. He sent me numerous pics along the way to show what he did. He did great work. Sadly he is now retired.