STEPS TO REPRODUCE
1. Create a custom Object.
2. Create 4 new attributes for this custom object(2 of type string (text1 and text2 and 2 of type number(num1 and num2)), add them to the Create and Edit page, also add them for Auditing.
3. Add 4 newly created attributes to the Audit trail.
4. Create a package for the custom Object and go to Hierachy and exlcude 2 attributes (in my case num1 and text1) from the package and package it.
5. Delete 2 attributes you left in the package (included and in my case it is num2 and test2) from the custom object in step number 4. Ensure you still have num1 and text1 in the audit trail
6. Now upload the content package via content -add ins(check the Migration Package checkbox).
7. Open the custom Object and go to the Audit Trail Tab, you will observe that only the attributes which were added as part of the package can be seen in the Audit trail.
Expected Results: Should not remove existing attributes from the audit trail.
Actual Results: it is removing existing attributes from the audit trail.
DE48348, Fixed in 15.6.1