Bootstrap Collapsed menu opening then immediately collapsing again

Uhg, it turns out I had a major brain fart! I was using a bootstrap 2.x CSS file, along with a bootstrap 3.x js file.

An in class is added when a click is triggered to open the menu but the collapse class isn't removed. Adding this css for overriding collapse properties worked for me:

.navbar-collapse.in {
    display: block !important;
}

You have Version Mismatch in bootstrap.css and bootstrap.js file/cdn. check once and you will realize the cause.