Link that the user included with their Answer Hub ticket: https://answers.unrealengine.com/questions/713209/levels-uneditable-editor-stuck-with-updating-asset.html
The file size is not maintaining a 3KB size after all actors are deleted from it and instead accumulating data with every actor that is added and deleted. After about 5 to 10 actors are added and removed, the file size sits around 66 to 70 some odd KB.
One odd thing to note is that if you quit, restart, and export the file again, the exported data is as expected. It doesn't contain the extra track information.
Head over to the existingAnswerHub thread and let us know what's up.