Timestamp precision issue-Oracle

I'm facing an issue related to timestamp precision in an Oracle table that’s used with Appian. The table has two timestamp columns:

• one with zero precision (Datatype - TIMESTAMP(0))

• one with six precision (Datatype - TIMESTAMP(6))

When I insert data into these columns without any triggers enabled, everything works as expected: the zero precision column doesn’t include milliseconds, and the six precision column includes milliseconds.

However, when I add a trigger to the zero-precision column, I get an error saying the actual timestamp precision is 7, but received 11 even though the column is defined with zero precision and the trigger only defaults it to SYSTIMESTAMP if null.

Why would the trigger suddenly cause exception , wanted to understand the logic better