1) Search functionality Finds `Eier/Forsikringstaker:
     SecurityError: Blocked a frame with origin "http://localhost:3000" from accessing a cross-origin frame.
  Error: Blocked a frame with origin "http://localhost:3000" from accessing a cross-origin frame.
      at setWindowDocumentProps (http://localhost:3000/__cypress/runner/cypress_runner.js:143709:42)
      at HTMLIFrameElement.<anonymous> (http://localhost:3000/__cypress/runner/cypress_runner.js:144418:11)
      at HTMLIFrameElement.dispatch (http://localhost:3000/__cypress/runner/cypress_runner.js:75099:27)
      at HTMLIFrameElement.elemData.handle (http://localhost:3000/__cypress/runner/cypress_runner.js:74907:28)
  2) Search functionality "after each" hook for "Finds Eier/Forsikringstaker":
     Error: Cypress command timeout of `4000ms` exceeded.
Because this error occurred during a `after each` hook we are skipping all of the remaining tests.
      at http://localhost:3000/__cypress/runner/cypress_runner.js:147599:25
  3) UI functionality "after all" hook for "Looks the same at start":
     SecurityError: Blocked a frame with origin "http://localhost:3000" from accessing a cross-origin frame.
  Because this error occurred during a `after all` hook we are skipping all of the remaining tests.
  Error: Blocked a frame with origin "http://localhost:3000" from accessing a cross-origin frame.
      at Context.<anonymous> (http://localhost:3000/__cypress/tests?p=cypress/support/index.js-945:1:3831)
Versions
4.3.0, Chrome 80 headless, Linux(image jenkins/jenkins:2.204.5-alpine)
          
You don't have to have iframes in order to get a cross-origin frame error. Please read our web security doc for explanations and workarounds: https://on.cypress.io/web-security
Unfortunately we have to close this issue as there is not enough information to reproduce the problem. This does not mean that your issue is not happening - it just means that we do not have a path to move forward.
Please comment in this issue with a reproducible example and we will consider reopening the issue.
          
I had a similar issue where I got an error message with localhost:3000
The error message was quite misleading as the problem might be one of the two:
in some rare cases, the Cognito Hosted UI redirected to their login page (in a different domain)
long(ish) request to an S3 completed at the end of the test and as it was from other domain it caused an error on the next test's beforeEach
I have added some debug messages to the Cypress source code as the localhost:3000 error message isn't correct.
I'll let you know what I found out.