page.evaluate returns empty object about playwright HOT 6 CLOSED

  const input = await page.locator('css=input');  
  await input.focus();
  await page.evaluate(() => {
    const config = {
      hasDropdownFlashed: false,
      observer: null
    };
    const dialog = document.querySelector('complex-object-combobox').shadowRoot.querySelector('dialog');
    config.observer = new MutationObserver((mutationList, observer) => {
      for (const mutation of mutationList) {
          if (dialog.style.display === '') {
            config.hasDropdownFlashed = true;                
          }              
      }
    });
    config.observer.observe(dialog, { attributeFilter: ['style'] });
    document.my = { config };
  });

  await page.keyboard.type('a');  
  await page.waitForTimeout(1000);
  await page.keyboard.type('r');  
  await page.waitForTimeout(1000);
  const hasDropdownFlashed = await page.evaluate(() => {
    console.log('hasDropdownFlashed: ', document.my.config.hasDropdownFlashed); // that value that will be passed to Node
    console.log('document.my.config.observer: ', document.my.config.observer); // actual observer in the browser
    document.my.config.observer.disconnect();
    return document.my.config.hasDropdownFlashed;
  });
  console.log('hasDropdownFlashed: ', hasDropdownFlashed);  // `true` in Node
  // expect config.hasDropdownFlashed to be false

from playwright.