cypress: getting random http response code 500

Current behavior & Steps to reproduce:

This works as expected:

cy.visit('http://localhost:8080/ui/st.bquadro/agent');
cy.get('.login-content input[type=text]')
    .type('admin')
    .should('have.value', 'admin');

cy.get('.login-content input[type=password]')
    .type('xxxx')
    .should('have.value', 'xxxx');

cy.get('.login-content .submit input[name=commit]').click();

cy.visit('http://localhost:8080/ui/st.bquadro/agent#dashboard', {
    auth: { username: 'admin', password: 'xxxx' }
});

but this gives some network errors (status code 500):

cy.visit('http://localhost:8080/ui/st.bquadro/agent#dashboard', {
    auth: { username: 'admin', password: 'xxxx' }
});

i’ve run our application with a debugger, and i’m almost sure our web server is not returning an error but a 200 OK.

the requests that fails are not always the same: but one of four files, just one of them succeeds. i’ve run cypress in debug mode and

Desired behavior:

test should not throw random 500.

Versions

windows 10 pro + chrome + cypress 3.0.2