Capcom has identified and fixed the cause for two major problems in the PC release of Monster Hunter World: Iceborne.
Update: Capcom has delivered the patch it announced earlier this week. The 254MB update released on Steam overnight, bringing the game's version to 10.12.01.
As promised, the patch allows the game to convert the old save format into the new one for players who had not played since the format was changed in late 2018. Those who ran into that infamous error should now be able to resume from where they left off, so start your game and try it out.
The only thing you're going to lose is keybind customisation, because the game's entire keyboard and mouse controls have been revamped. Controls will be reset to their current default values. Capcom said that you should ignore the "Failed to load keyboard setting presets. Data is corrupt" message, if you receive it.
As for the CPU problem, the patch lowered CPU utilisation during gameplay, so you should no longer run into stutters caused by unusually high utilisation. The effect of this will vary, however, depending on your setup.
Read on below for the original story.
Original story: Shortly after launch, Monster Hunter World: Iceborne players on PC ran into a number of issues they've since been trying to solve. The biggest and undoubtedly most egregious is a bug that put save files at a risk of deletion.
Players suggested at the time that it had something to do with a file format change Monster Hunter World's save files had undergone, which meant that those who didn't play the game between that change and Iceborne's launch ended up with save files the game couldn't recognise.
Capcom didn't comment on that issue specifically then, but have thankfully now revealed that a fix is in the works. In a Steam post, the developer confirmed the running theory, adding that the problem specifically occurs when save data hadn't been updated since October 30, 2018.
Capcom advised players to shut down the game when the infamous error message appears, so it sounds like the fix will convert the outdated save files of those affected to the new format.
Another widely reported problem has been a strange dip in performance and frequent stutters after the release of Iceborne, even for those who do not own the expansion and haven't visited the Hoarfrost Reach region. Capcom acknowledged the issue at the time, and has now also confirmed a fix is being worked on.
The cause, once again as players suspected, is unusually high CPU utilisation. Both of these problems will be fixed in patch 10.12.01, which Capcom says is due "in the coming days."
If you've not been running into these problems yourself, you're probably at a point now in Iceborne where you'll looking to farm for the never-ending quest for better gear. Our guides for Master Rank materials, the new weapon augments and the top weapon trees in raw damage should all come in handy.