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I don't WhatsApp so I really don't know much of anything about it. I am a bit surprised that you would have to bring a folder with you to a new device, especially since you can view the conversations online and see all of the same stuff without any additional folders. So my feeling is one of a few things is happening;
Something has renamed the photos, possibly the ones in the migrated folder. So img06271 was daffodils in the park got renamed and an image with the same name or similar name has taken its place.
When you installed the app it created its own WhatsApp folder, which it most likely did even with the migration, and it is populating the image holes with images from the folder it created when installed.
It's totally ignoring your migrated folder and using other images as placeholders for missing images.
You never said if these were images from your end or ones that were shared with you?
Since you can view the conversations online with any migrated folder, I would uninstall or sign out of the app, remove the migrated folder and sign back in or install the app and allow WhatsApp to do what it does without any help. There's a very good chance that the app knows what's best without any help.