The same issue happens for me. It appears that since the last few update the Tabs have been “broken”. I’ve only recently noticed it though. I use it extensively on my website to separate different elements.
Some of the pages affected:
https://wp.me/P2Vm8L-g6
https://wp.me/P2Vm8L-mm
I’ve been looking for an alternative, but nothing’s on a par with this plugin. It’s unfortunate.