You didn't follow the first step. Disable the indicated plugin and it will remove the phantom tab. The phantom tab, and that plugin, is a remnant of the old way that vb4 dealt with tabs. This was changed in Vb4.1 but this plugin has not been updated since then.
There's also a third fix, step 1 in post
https://vborg.vbsupport.ru/showpost....&postcount=742, the second and third steps are the same as the ones I'd posted earlier.
You also potentially have other conflicts as you're using a custom style which have other issues that are causing problems. Always test with the vbulletin default style.