To reproduce the issue run the code below and select "All Files" file format in JFileDialog.
More than one "Aqua L&F File Loading Thread" (see AquaFileSystemModel.FilesLoader) is run.
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import javax.swing.JFileChooser;
import javax.swing.SwingUtilities;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileNameExtensionFilter;

public class JFileChooserSample {

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(JFileChooserSample::createAndShowGUI);
    }

    private static void createAndShowGUI() {
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setAcceptAllFileFilterUsed(true);
        fileChooser.setDialogType(JFileChooser.OPEN_DIALOG);

        FileFilter txtFilter = new FileNameExtensionFilter("Text files", "txt");
        fileChooser.addChoosableFileFilter(txtFilter);
        fileChooser.setFileFilter(txtFilter);
        fileChooser.showOpenDialog(null);
    }
}
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