In this configuration activity you are able to globally activate or deactivate document splitting and also turn it on or off per company code.
IMG Path: Financial Accounting (New) -> General Ledger Accounting (New) -> Business Transactions -> Document Splitting -> Activate Document Splitting
Tables: FAGL_ACTIVEC, T8G01, T8G01T, T001, FAGL_SPLIT_ACTC
When you initially open the transaction you will get following screen. You are able to activate or deactivate for all company codes. You are also able assign constant and check other options according to your requirements. To activate or deactivate per company code click on the second folder icon “Deactivation per Company Code”,
Find you company code and see if the check-box is flagged. If it is flagged the document splitting is not active for that company code.