DB2 - ODBC - transaction problem

Most of the information I found on this error points to errors in the procedure, but you've already stated it works in other environments. Are you using the same account to connect to the database in those other tools as the account which is configured for CodeIgniter?

I've also found a few references in IBM's Knowledge Center about known issues which might cause these errors, but they're specific to using certain APIs or features, so the workarounds they provide may not be relevant. Most of them do seem to suggest setting autocommit mode or issuing a commit/rollback before/after the offending command in the stored procedure. Searching for "php SQL0428N" seemed to return a few potentially useful results.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide