After waiting almost four months for Monster Hunter World: Iceborne, the first paid expansion for Capcom's best-selling Monster Hunter title ever, PC players have booted up their newly updated game to find they can't access old save files. The exact cause of the bug hasn't yet been pinned down, but for the sake of safety, anyone who hasn't logged into Iceborne on PC yet should immediately back up their save data before attempting to log in.
The current suspect for the save data loss is the use of mods that are no longer compatible with Monster Hunter World: Iceborne and the patches that came with the recent launch. This means even players who haven't bought the new content should be cautious when booting up the game, as the new performance updates for the base game all together might be what is causing the issue.
What seems to be happening, according to reports on Steam discussion boards and Reset Era, is that when the game first loads after installing the Iceborne expansion, it checks to see if there is a compatible save available. However, if the game finds a save that isn't compatible, the data will be deleted and replaced with a brand new file that unfortunately doesn't house the player's characters, achievements, or items. Considering how long it can take to grind up every piece of gear from the various monsters in Monster Hunter: World, losing that progress can mean giving up hours of gameplay, with some lost items blocked by limited events.
The most common theory for the root cause of this issue involves mods that players may have installed that are no longer compatible with Iceborne. Some players and members of the modding community have even gone so far as to suggest players should rename or delete nativePC if they don't want Iceborne to brick their systems as soon as they boot up. It may be hard for some players to say goodbye to some of the best mods available to Monster Hunter World, but at this point it's either go without mods until they're updated for the newest version of the game or risk losing save data.
If this latest bug unfortunately means that PC players have to wait even longer to dive into Monster Hunter World: Iceborne, then it's better that it be done by choice rather than necessity for now. PC players should be careful and make sure to check and recheck any mods they may have installed for their game, regardless of how complex or simple it may be. However, at the time of writing, Capcom has yet to make an official statement about the lost save files, so every theoretical cause at the moment isn't much more than hearsay and speculation.
Monster Hunter World: Iceborne is available now for PC, PS4, and Xbox One.
Source: VG247