I swear, the devs at Guerrilla Games truly are wizards! They quickly identified a small issue that came about from Update 1.45 and have solved the problem with Update 1.46.

Patch note details:

Patch 1.46 for Horizon Zero Dawn: The Frozen Wilds is live now. This patch fixes a technical issue that was introduced with Patch 1.45.

If you encounter an issue while playing Horizon Zero Dawn, please try reloading a recent manual save, quicksave or autosave from the “Load” menu option. If the issue persists, please record a video or take screenshots of the area where it occurred and your location on the map using the Share button on your controller, and forward them to us for further investigation.

CRASH FIXES

• Fixed a crash that would occur for certain players when trying to load a save where the player had an opened treasure box in their inventory containing a modification and other items.

Update 1.45 solved many issues, you can read about it here.