Not sure if this is already fixed in an upcoming release, but I’d like to add my two cents.
Best way that I have found to replicate this is to make a repeater-field with two required text fields and a true/false which is used for conditional logic.
Set one textfield to show when the true/false is unchecked and hide the other. viceversa for when the true/false is checked.
IE;
Textfield A*: show if value is equal to unchecked.
Textfield B*: show if value is equal to checked.
If you then reload the edit page it wil invalidate the block and prevent the entire page from being updated. When you nibble on the true/false checkbox (or kick any field in the repeater) it will update and presumably see the conditional logic and validate the field again, allowing you to update the page.
Although, it doesn’t seem to be limited to just repeaters, as similar logic in the block itself has problems too.
This is in combination with ACF’s Gutenberg block functionality by the way.
