This seems odd to me that you are experiencing this with multiple devices in your account. This other device, has it always shown up as a Core? One thing is for certain --> if a device is in a product and gets removed from it, it will return to the device type that the product is based on.
It seems like somehow someway, these devices found their way into your Core-based product. Then they were removed, and the cloud labeled them as a Core. I'm not entirely sure how this would have happened, as the cloud will block imports of devices that are of the wrong device type (you experienced this first-hand).
But, I do have one theory on how this could happen where a device gets added to a product without being officially imported. Were the 2 devices included in this thread:
3c0042001951343334363036 ever running firmware that included the
PRODUCT_ID macro with your core-based product's ID? That would look like this
If these devices were running product firmware from this product, and your product configuration was set to "Auto-approve" unrecognized devices, this could have resulted in these devices being added to your Core-based product unintentionally. Then, when you removed them, they were labeled as a Core.
Does this at all sound possible?