Embedding two content blocks results in rendering an error message

Problem/Motivation

Steps to reproduce

Embed two content blocks in the same text area ("long text with summary" aka "body")-
Both embed codes work fine if they are inserted alone.

If both are added, the page renders an error message.

Using Olivero-based theme with some CSS changes on Drupal 11.1.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes