Translating records with FAL relation where allowLanguageSynchronization set to true
When translating a record with a immage (FAL relation) where allowLanguageSynchronization is set to true in the TCA configuration typo3 throws the exception #1486233164: Child record was not processed and the record gets some new immage relation entries
Easiest to Reproduce with the georgringer/news extension
Steps to reproduce:
1. Create a new (news) record, set language to [All]
3. Add immage as fal relation,
5. Set language to Default 
7. Translate (In the News Administration section)
8. Admire the Exception/CMS/1486233164 page and the new copies of the FAL relation
Tested in Typo3 8.7, 9.5 and 10.0
#1 Updated by Christian Eßl 2 months ago
We got the same problem here with the pages -> media fal field. Trying to translate such a page produces pretty chaotic results by duplicating all image relations.The same error occurs when we go to the Access module and try to change the access permissions of such a page. (Click for example "New pages" icon)
- The server will answer with a 500 error and the message "Child record was not processed"
- All inline image relations were duplicated.
When setting allowLanguageSynchronization to false, the problems disappear.