IMPDP twice with same Oracle EXPDP dumpfile with different results?

At my work, we receive data in the form of an Oracle dumpfile generated by an EXPDP command using Oracle DB 11.2.0.4.0. We import it using IMPDP into an Oracle DB (same version) set up with roles, users, and tablespaces set up by a SQL ddl file provided by the data provider. However, the import log shows that the same number of rows are not exported all the time. This affects about 5% of the tables, typically the same ones. The differences in row count are usually within a percent of each other. We do not change anything about the processing.

The IMPDP command we use is:

impdp user/passwd DIRECTORY = IMPORT_DIRECTORY DUMPFILE=<dumpfile> SCHEMAS=<list of schemas> CONTENT = ALL

After every import, we clear the database by dropping all roles, users, tablespaces, and profiles generated in the SQL ddl file.

Any advice would be appreciated.