Is it necessary to use merge policy with CoreData and Allows external storage to avoid crash?

Question

I use CoreData + NSPersistentCloudKitContainer to backup my model. One of my NSManagedObject has a picture stored as Binary Data and Allows external storage checked.

It's very random but sometimes when i call context.save() i get a merge conflict even if i don't have edit this object. In fact i just try to create a new object (different type as the one with conflicts) and the crash is on another object.

Everyting is the same value except the self reference of External Data Reference:

    ERROR AppDelegate.saveContext():262 - Unresolved error Error Domain=NSCocoaErrorDomain Code=133020 "Impossible de fusionner les changements." UserInfo={conflictList=(
    "NSMergeConflict (0x600002c62f40) for NSManagedObject (0x60000158da40) with objectID '0x816659a4c358c32f <x-coredata://CEAE3B14-5782-4C18-AAE8-B05D91CFEC8A/Aquarium/p5>' with oldVersion = 56 and newVersion = 57 and old object snapshot = {\n    albums = \"<null>\";\n    aquaID = 6;\n    dateDeCreation = \"2022-01-15 18:24:00 +0000\";\n    imageData = External Data Reference: <self = 0x60000158db80 ; path = 1B9355A6-4101-479D-81F1-DFC106BBCD75 ; length = 1617016>;\n    nom = 11321;\n    volume = 60;\n} and new cached row = {\n    albums = \"<null>\";\n    aquaID = 6;\n    dateDeCreation = \"2022-01-15 18:24:00 +0000\";\n    imageData = External Data Reference: <self = 0x6000015ccf50 ; path = 1B9355A6-4101-479D-81F1-DFC106BBCD75 ; length = 1617016>;\n    nom = 11321;\n    volume = 60;\n}"
), NSExceptionOmitCallstacks=true}, ["NSExceptionOmitCallstacks": 1, "conflictList": <__NSArrayM 0x600003a25ec0>(
NSMergeConflict (0x600002c62f40) for NSManagedObject (0x60000158da40) with objectID '0x816659a4c358c32f <x-coredata://CEAE3B14-5782-4C18-AAE8-B05D91CFEC8A/Aquarium/p5>' with oldVersion = 56 and newVersion = 57 and old object snapshot = {
    albums = "<null>";
    aquaID = 6;
    dateDeCreation = "2022-01-15 18:24:00 +0000";
    imageData = External Data Reference: <self = 0x60000158db80 ; path = 1B9355A6-4101-479D-81F1-DFC106BBCD75 ; length = 1617016>;
    nom = 11321;
    volume = 60;
} and new cached row = {
    albums = "<null>";
    aquaID = 6;
    dateDeCreation = "2022-01-15 18:24:00 +0000";
    imageData = External Data Reference: <self = 0x6000015ccf50 ; path = 1B9355A6-4101-479D-81F1-DFC106BBCD75 ; length = 1617016>;
    nom = 11321;
    volume = 60;
}

I suspect the data reference changed between the time the application loads and the first time I call the backup. But the length is the same since this value has not been changed on the user side, so I don't understand why the reference changes.

I use no merge policy right now and it just don't save.

Can i use NSMergeByPropertyObjectTrumpMergePolicy to be safe or should i find why the reference changed ?