Cypress opens test runner on localhost:XXXXX and then jumps to configured base url

I have a cypress project for testing a UI, and the baseUrl is configured as "http://localhost:3000" What is happening is that when I launch the test runner, first it point to "http://localhost:XXXXX/_/..." (with a random port each time), and then when it is in the middle of the first test execution, the browser refreshes and shows pointing to localhost:3000, and starts over

Anyone has an idea of what could be causing this?