It sounds like you are trying to upload a browser/HTML5 game, so it would be played on your page? If yes, this is due to zip file requirements.
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You can try upload the game without making it a browser game.
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make a copy of your current project and delete part of the level. Do the zipping again and see, if the chunk error disappears. this way you will know if it is truly the level map, not something else.
It is hard to advice anything without knowing technical details, you may succeed getting faster help from the official discord, if you haven’t tried there yet.