The new CF editor enforces stricter validation rules than the old editor. Open the browser's developer console (F12) when attempting to save and check for specific validation error messages that may reveal which fields are failing validation.
CF created through bulk import tools may not have complete metadata (see empty required fields) or validation attributes that the new editor expects. The old editor is more lenient with missing or incomplete field data, while the new editor validates against the CF model more strictly.
If you save a CF using the old editor, does the new editor allow autosaves, or do you continue to encounter validation failures?
If so, try creating a test case comparing a fresh CF created manually versus one from the AWS bulk import tool to identify exact structural differences.
https://meticulous.digital/blog/f/migration-to-the-new-content-fragment-editor-in-aemaacs?blogcatego...
https://experienceleague.adobe.com/en/docs/experience-manager-learn/content-fragments-console/editor...