Toolbar showing in website without log-in

Hi folks, sorry in advance for my ignorance.

A few days ago my website has started to show the administration bar even when you arrive as a non-logged user to visit the website.

The only significant change is that I installed a plugin to add php code (code snippet), but I have a test site where I do the tests before going live and there have been no problems with it.

Had someone experience this kind of issue? How can I fix it?

Thanks in advance!