I have multiple locales, but the example is copying (creating) a document from one locale to other using "Copy to another locale" functionality.
I'm not copying to multiple locales at one time, but from (using your example) from "Arabic - Bahrain" to "Arabic - UAE"
when copied to other locale it overwrites an existing document - copying from Locale_1 to Locale_2. Locale_2 does not have that document (eg. product), but when copied from Locale_1 it overwrites some other product on Locale_2 with product data from Locale_1.
I compared document ids. - The way I figured point 3. happened is when i compared document id (unique id which is assigned by prismic when document is created).
Since we daily copy a lot of documents between locales, and the outcome seems to be unpredictable, we'd appreciate if you found time for zoom call so that we can demonstrate what we are dealing with.
Could you please share your repository and Custom types name that you are copying to another locale with me? You can send me a private message. I'll talk to my dedicated colleague responsible for taking Zoom calls and let you know.