An AS400 Agent will start and then end immediately without any errors in the logs.
If the Agent is on v12 or higher this is likely due to the fact that the KEYSTORE parameter is empty, as this parameter is required with V12 and higher.
From the .ini:
Fill the Keystore parameter with the proper value. The parameter needs to be filled with libraryname/KEYSTORE. If the libname is AUTOMIC then the proper value would be AUTOMIC/KEYSTORE.