How can I find out there is a automatic archive is going on???
You can check it by two ways, basically:
- Type "archive log list" on SQL*Plus when connect as sysdba
- Your database will hang when a log switch try to overwrite an unarchived redo log.

That's not your case. I'd bet it's a lock issue, but since you told us there's nothing and the database is running fine, you may check if it is something related to the application.