Whenever there is an invalid field hidden inside of a tab (container), there is no way of knowing. Ideally, the tabs would be marked depending on their invalid state or even better: being activated instantly.
While there is probably some workaround, I think a native solution would be the best fit.
Hi @emozio,
I agree, if a form is not visible but has invalid input fields it would be very useful for users to know where the form and field are located.
I can definitely make a feature request but the UI team may have this as a lower priority for a build in fix. A native solution is definitely the ideal goal and I will keep you updated on any word I hear on the ticket 
A potential work around in the short term would be to iterate through the tabs, then iterate through the form inputs to check if any of the inputs have invalid: true in their state.
Then you could have a modal or text component above the tabbed container to read out to the user what is invalid and which tab it is under 