The default value of the Priority attribute can not be removed. At saving it always reverts. In custom number-type attributes that have a validation range and are not required, the default value can be removed.
STEPS TO REPRODUCE:
1. Go to Classic > Administration > Studio > Project object > Attributes tab
2. Locate and edit the Priority attribute
3. Remove the Default value and save
Expected Results: The default value to be removed
Actual Results: The default value reverts back
This is caused by DE116273
This is fixed in 16.3.0 and targeted to be backported to 16.2.3.1