[Sulu] cannot save page changes

When this issue occurs, in Symfony logs exists this message:

request.CRITICAL: Uncaught PHP Exception Sulu\Component\Content\Form\Exception\InvalidFormException: "[authored] This value is not valid

The solution is to upgrade to Sulu v1.6.22, it downgrades Symfony from 3.4.17 to 3.4.14.

Appeared in v1.6.21