I sincerely apologize for the inconvenience this issue has caused.
Based on similar reports, this problem is likely caused by corrupted or unreadable characters in the save data (.txt) file. In particular, it may occur when the game is played in a non-Japanese Windows system environment, which can result in character encoding issues within the .txt file.
I kindly ask you to check your Windows system language settings. Running the game in a Japanese system environment may prevent this issue from occurring.
I truly apologize for the trouble and appreciate your understanding.