Package became INVALID

I am in trouble with a package (note: this package uses a db_link in the code).
I created it, did
alter packave pck compile;
alter package pck compile body;​

I check status it via :
select object_name, status, object_type from user_objects where status = 'INVALID';
The result of this query is : VALID for spec and body.

After It, I don´t run anything and I check again and the package body became invalid.

The package is compiled in the Oracle 12c (12.1.0.2.0)

​Any idea ?
How can I see who is putting the package in the INVALID status ?

Regards
Eriovaldo

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