I was not able to test this elsewhere, only on XWiki. And I am not sure if the problem is XWiki or Grist.
But when using tabs on XWiki and iFrames inside the tabs, I get some weird XWiki rendering errors.
it usually requires the user to click in a widget then click on other widget, to fix the 2nd clicked widget. Expanding a widget fixes it too, and when closing the expanded view, all the widgets in a page get fixed too.