Essentially, Joy-Con drift is the issue of the controller joystick inputting directions even when it’s not being moved by the player. To put it short, it’s the result of accelerated wear and tear, and the lawsuit filed by the law firm Chimicles, Schwartz Kriner & Donaldson Smith, claims alleged defects in the Joy-Con controllers that lead to the issue.
Originally, the topic popped up once again recently on Reddit, with a survey later done by Chimicles in order to get more data on this issue. (Note: The site is currently down, likely from server stress.) Now, it seems that Nintendo may be facing charges. The issue itself has never been addressed by Nintendo themselves.