You’ve removed the wrong elements. See the code i gave above, it’s the ‘gst_tabs_nest_text_st1_tab_menu__item’ that needs removing, not the tab inside. The tab inside is the important part as it’s a core part of the tab structure, the menu item part is the custom bit is causing the issue.
if no luck, just add new tabs, and copy the classes over. The new one will work out of the box and it’ll only take a second to move the content over.