Missing data in Oracle database when there is bulk insertion in the table

Oracle version: Oracle 11g Standard edition

Our application inserts approximately 1 million events per day in to the table.

During these processes, we are seeing missing data that we can find using gaps in sequence number column (called INDEX).

Whenever there is gap in INDEX column, there is also missing data in table.

Now, we need to find whether this data failed to insert into oracle table or deleted from oracle.

In Our application log files, we are not seeing any specific errors. Below is the random error which we observed in our log files.

“Oracle Error (100)”

Do you suggest any way or oracle log files to check for this use case?