John Mueller from Google was asked if having invalid markup for structured data would lead to having a manual action. The answer is no, John said "Just having invalid markup wouldn't be a cause for a manual action there."

If the markup goes against Google's structured data guidelines - then sure, you get get a manual action. But if you just used invalid markup, then no, that wouldn't cause a manual action.

You still need to fix the invalid markup, because Google might not show the rich results in search because Google cannot understand it.

Here is John's tweet:

If the error in structured data results in the structured data not being compliant with our guidelines, then that's possible. Just having invalid markup wouldn't be a cause for a manual action there. — 🍌 John 🍌 (@JohnMu) August 27, 2019

Froum discussion at Twitter.