Updating from 14.9.1 to 15.4.0, unresolvable validation errors because of anchors / id attributes

[lakeme]

Description

After updating from Gutenberg 14.9.1 to 15.4.0 I get a bunch of 'unresolvable' validation failed errors. Unfortunately the logs in the console were not helpful at all.
After some investigation I found out that the validation errors come from simple anchor tags.
In Gutenberg 14.9.1 when adding an anchor tag to a block this results in

Gutenberg 14.9.1

<!-- wp:group {"backgroundColor":"tertiary","layout":{"type":"constrained"}} -->
<div id="test" class="wp-block-group has-tertiary-background-color has-background"><!-- wp:heading -->
<h2 class="wp-block-heading">Test</h2>
<!-- /wp:heading --></div>
<!-- /wp:group -->

When I paste this code into an editor with Gutenberg v.15.4.0 this results in one of these
'unresolvable' validation failed errors (after a reload)
I found that that is simply because of the missing "anchor": "test" in the attributes.

Gutenberg v.15.4.0

<!-- wp:group {"align":"wide","backgroundColor":"tertiary","layout":{"type":"constrained"},"anchor":"test"} -->
<div class="wp-block-group alignwide has-tertiary-background-color has-background" id="test"><!-- wp:heading -->
<h2 class="wp-block-heading">Test</h2>
<!-- /wp:heading --></div>
<!-- /wp:group -->

That is an annoying situation since that does not only removes the anchor tags but also
requires to redo all the editing again.

Step-by-step reproduction instructions

1. wp plugin install gutenberg --version=14.9.1 --force
2. add a group block with an anchor tag / HTML Anchor and some child blocks inside
3. copy the block markup
4. wp plugin update gutenberg (update to 15.4.0)
5. paste block markup, save and reload site, check console

Screenshots, screen recording, code snippet

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

No

[t-hamano]

@lakeme

Thank you for the report.

This problem should occur in all blocks that want to support the anchor. The same problem was reported in #48232 and a fix is being attempted in #48232.

[t-hamano]

Hi @lakeme,

This issue is due to the dynamic block anchor support added on the Gutenberg plugin. We have removed this feature from the Gutenberg plugin so this issue will not occur.

Instead, I have submitted #51402 to consider re-adding anchor support to dynamic blocks,