It sounds to me like they tried to fix a bug where she ate bullets through walls and ended up breaking her completely. Now if any part of DM touches a wall, the whole DM stops working even the part that’s not in or behind the wall. She still gives sound effects, voicelines, and visual effects indicating deletion, but the bullet still does full damage.
YourOverwatch has a video displaying this, and someone went into it in extensive detail in the bugreport forums.