Thunder Video
This is because the player cannot distinguish "hard subtitles", that is, "sticker subtitles". Among the video files compressed by major subtitle groups, the subtitle files have been pressed onto the screen, such as the following picture:
Thunder Video
If the player cannot parse the subtitle stream in the file, it will consider that the file does not have embedded subtitles, and will start the automatic online subtitle matching function.
At this point everyone will see the double subtitles situation.
Once double subtitles are found, you can manually turn off subtitle display (right-click - subtitles - closed subtitles).