If you delete a customer profile and that customer later opens an email, the email open-tracking pixel can create a new profile. The recreated profile does not restore the original customer identifiers so that it may appear with empty IDs.
This behavior is expected, and a profile without identifiers can be created this way.
Verify the case
Use these steps to confirm whether this is the reason you see profiles without IDs:
Check whether the affected profile was deleted earlier.
Check whether the profile has
campaignevents with status opened.If the profile shows no events now, check whether the
campaignevents have already expired.
Confirm or investigate
If these checks match, treat the profile as a recreated record rather than a separate profile-creation issue.
If they don't match, continue investigating other possible sources of profile creation.