photos_time_warp VS add_photo_locations_from_google_history

I think the most likely thing that has happened in your case is that the data in the Photos.sqlite database file has been corrupted somehow--likely some kind of bug in Photos.app. So when Photos reports the date on a photo, it's retrieving that date from the database, not from the actual image file on disk. Thus, it's possible the date/time of the photos themselves is still preserved in the EXIF data of the original images. The Photos Time Warp tool has an option to read the date/time from the EXIF data and reset it in the Photos database to match. This tool requires a level of comfort with the command line so I wouldn't use it if you're not comfortable running commands in the Terminal but it is one option (the only one I know of) that might be able to restore the correct date/time for your affected photos by reading the data from the EXIF data of the original images.

I did something similar to add missing locations from my Google takeout history.

If geolocation truly isn't working in South Korea (maybe Apple has some agreement with South Korean government?) it's almost certain that any Google app you have is still tracking your location and reporting that to Google (unless you've turned this off). In that case, you could make sure you open a Google app at each location to track the location then when you get back you could use this script of mine to grab the location data from your Google history and insert it into the photos. (This is a bit of a hack and assumes some level of comfort working in the command line)