I also read this thread
https://www.shape5.com/component/option,com_smf/Itemid,75/topic,45496.0/ and tried the suggestion. I noticed that S5 Tab Show v2 was included in the template - I downloaded S5 Tab Show v3 from the link (latest) and updated it. No change.
The tab appears if I hover over the selector box, otherwise it is blank and does not animate.
This is on Joomla 3.7.2, PHP 7.0.20
I did have the site "offline", but changing that did not fix the problem.
I also tried changing the position to above_columns_1 and it works there but of course is not what I want, or how the template was designed.
The same issue happens with Custom 2 Tab Show, in position custom 2, which also uses S5 Tab Show module.
This is on my site here:
https://infotechdesign.website