Not claiming any expertise in this area, here is what I’d look at:
1). Is the “identity” of the ODBC link consistent with the “identity” of the journaling process?
In many situations like this, what you want to do in a production environment is have a “thread” on the AS400 which acts as a server to the database, accepting transactions from any legitimate user.
When you set up the ODBC link in an “end user” MS Access environment, you may be accepting default settings for that link which could make it compete with the “Journal” thread for access to the database.