This is according to a report from gamers on Reddit in which it has been discovered that hackers are corrupting the save files of other players. According to the post, “Currently there is a hack doing the rounds whereby invaders will alter your save files in some way, causing you to enter a permanent, instant death-loop. There is seemingly no real fix for this, and so it is recommended to back up your saves as often as possible for the foreseeable future as a precaution.”
If this issue sounds familiar, it is because it was also an issue that previously affected Dark Souls 3, a game made by the same developer as Elden Ring. At the moment there has been no comment from either the developer, FromSoftware, or its publisher, Bandai Namco. The post on Reddit has shared a method that could potentially solve the issue, but it feels more like a temporary solution until it can be properly patched.
So until a patch has been released for the game that addresses the issue, players are advised to either backup their save files as often as possible, or play in offline mode until it is fixed.