App.jsx

import { useEffect, useState } from 'react';

function App() {
  const [on, setOn] = useState(false);
  const [remounts, setRemounts] = useState(0);
  const [showDisappearingButton, setShowDisappearingButton] = useState(true);
  useEffect(() => {
    let interval, disappearingInterval, appearingInterval
    if (remounts < 1000) {
      interval = setInterval(() => {
          setOn(!on);
          setRemounts(remounts + 1);
      }, 0);
      setTimeout(() => {
        disappearingInterval = setInterval(() => {
          setShowDisappearingButton(false);
        }, 10);
      }, 1);
      appearingInterval = setInterval(() => {
        setShowDisappearingButton(true);
      }, 3999)
    }

    return () => {
      clearInterval(interval);
      clearInterval(disappearingInterval);
      clearInterval(appearingInterval);
    }
  });

  return (
    <div className="App">
      { showDisappearingButton ? (
          <button id="disappearing">disappearing button</button>
        ) : null
      }
      {on ? (
        <div id="parent">
          <button id="remounting">remounting</button>
          <button className="remounting" id="remounting-2">remounting</button>
          <button className="remounting" id="remounting-3">remounting</button>
          <input type="checkbox" className="remounting" id="remounting-4"></input>
          <input type="checkbox" className="remounting" id="remounting-5"></input>
        </div>
       ) : null }
      {!on ? (
        <div id="parent">
          <button id="remounting">remounting</button>
          <button className="remounting" id="remounting-2">remounting</button>
          <button className="remounting" id="remounting-3">remounting</button>
          <input type="checkbox" className="remounting" id="remounting-4"></input>
          <input type="checkbox" className="remounting" id="remounting-5"></input>
        </div>
       ) : null }
      <button id="not-remounting">not remounting</button>
    </div>
  );
}

export default App;

error.txt

CypressError: `cy.then()` timed out after waiting `4000ms`.

Your callback function returned a promise that never resolved.

The callback function was:

() => originalFn(...args)

https://on.cypress.io/then
      at <unknown> (http://localhost:6543/__cypress/runner/cypress_runner.js:118353:75)
      at tryCatcher (http://localhost:6543/__cypress/runner/cypress_runner.js:1807:23)
      at <unknown> (http://localhost:6543/__cypress/runner/cypress_runner.js:4186:41)
      at tryCatcher (http://localhost:6543/__cypress/runner/cypress_runner.js:1807:23)
      at Promise._settlePromiseFromHandler (http://localhost:6543/__cypress/runner/cypress_runner.js:1519:31)
      at Promise._settlePromise (http://localhost:6543/__cypress/runner/cypress_runner.js:1576:18)
      at Promise._settlePromise0 (http://localhost:6543/__cypress/runner/cypress_runner.js:1621:10)
      at Promise._settlePromises (http://localhost:6543/__cypress/runner/cypress_runner.js:1697:18)
      at _drainQueueStep (http://localhost:6543/__cypress/runner/cypress_runner.js:2407:12)
      at _drainQueue (http://localhost:6543/__cypress/runner/cypress_runner.js:2400:9)
      at Async._drainQueues (http://localhost:6543/__cypress/runner/cypress_runner.js:2416:5)
      at Async.drainQueues (http://localhost:6543/__cypress/runner/cypress_runner.js:2286:14)
  From Your Spec Code:
      at Context.eval (webpack:///../src/cypressCommands.ts:123:7)

test.cy.js

describe('test', () => {
    it("doesn't error when no remounting", () => {
        cy.visit('/')
            .get('button#not-remounting')
            .click();
    });
    it('errors with a single selected remounting element', () => {
        cy.visit('/')
            .get('button#remounting-3')
            .click();
    });
    it('errors with multiple selected remounting elements', () => {
        cy.visit('/')
            .get('button.remounting')
            .click({multiple: true});
    });
    it('errors with multiple selected remounting elements and selectors', () => {
        cy.visit('/')
            .get('#remounting-2, #remounting-3')
            .click({multiple: true});
    });
    it('errors when a Cypress command that handles multiple DOM elements tries to handle multiple remounting elements', () => {
        cy.visit('/')
            .get('input.remounting')
            .click({multiple: true})
    });
    it('(sometimes) errors from Axe when an element is detached and not reattached with the same selector', () => {
        cy.visit('/')
            .get('button#disappearing')
            .click()
    })
});