While Diablo IV's launch was relatively better off than its predecessor, the game still has its share of bugs. However, a not-so-insignificant number of players (myself included) have been afflicted by a memory leak. A cursory Google search reveals the problem has existed since the game's open beta. Thankfully, a Blizzard employee has finally addressed the issue and promised a fix.
On a Reddit thread about the topic, Adam Pez, Blizzard's Global Community Development Director, promised Diablo IV's memory leak will be fixed via the big patch on July 18, two days before Season Of The Malignant drops. Not everyone seems to be affected, but the leak appears to be system agnostic, as people with both high-end and dated hardware have reported the issue.
For now, the only solution appears to be restarting Diablo IV every 30 minutes and turning off high-quality textures. Players are also complaining about a VRAM leak, albeit in much smaller numbers. Nevertheless, it has resulted in an immersion-breaking experience, which can get frustrating, especially when Diablo IV crashes halfway through a Nightmare Dungeon.