More tag from classic editor displays warning in Gutenberg

[bradyvercher]

Issue Overview

When opening a post with a more tag in Gutenberg that was originally created in the classic editor, a warning is displayed and block validation errors appear in the console.

Steps to Reproduce (for bugs)

1. Create a new post in the classic editor with a more tag
2. Open the post in Gutenberg

Expected Behavior

I expected to be able to view and edit my content without warnings.

Screenshots / Video

[danielbachhuber]

I can reproduce this issue in Gutenberg 2.0.0. When I open an existing classic editor post with <!-- more --> tag in Gutenberg, this is what I see:

[aduth]

Potentially related: #4038

[danielbachhuber]

@mcsf What was the resolution?

[mcsf]

#5061 substantially changed the way More tags are handled. There's room for refinement, but so far it seems that the current issue and its sibling #4038 no longer apply.