After installing the Seeker, Slayer, Survivor DLC, I loaded up the game and found that the game now had some sort of filter on it that made the graphics look like they were being displayed on a CRT monitor. Horizontal and vertical lines cross the screen, becoming more or less pronounced as I zoom in or out. There's also flickering, as though the lighting can't decide whether to be bright or dark, changing rapidly as I move the section of the map I'm viewing from side to side.
Below is a screenshot showing the issue.
Edit: The graphics issues don't appear in the main menu or on the loading screens, or even in the inventory or character menus in-game. I did verify my game cache, and everything verified.
Edit 2: Scrolling in five steps from fully zoomed out causes the grid/cross-hatching to shift larger and larger until finally it vanishes, but scrolling out from completely zoomed in does not have the same result. Edit 3: Pinpointed the issue, it only occurs when the graphics are set to high quality.