Here are a few potential factors to consider:
Image size or format: The issue may be related to specific image files that are causing the error. Check if the problematic images have any unusual characteristics, such as large file sizes, non-standard formats, or special metadata. It's possible that certain images trigger a problem within the RTE's processing or rendering.
Browser compatibility: Verify if the issue occurs consistently across different web browsers. It's possible that the problem is specific to a particular browser or its version. Test the RTE functionality with various browsers (e.g., Chrome, Firefox, Internet Explorer) to see if the error is browser-dependent.
If none of these solutions resolve the issue, it's recommended to contact Sitecore Support for further assistance. Provide them with as much information as possible, including the version of Sitecore, the browser used, and the steps taken before the error occurred. They should be able to assist you further in diagnosing and resolving the issue.