Few things to check:
Can you restart (="Restart after error") the workflow for example from SWI2_DIAG? If the workflow continues, then the issue might be with WF-BATCH user.
Can you see another error message(s) (than the one in WF log) in SWI2_DIAG?
Does the user WF-BATCH have SAP_ALL and SAP_NEW authorizations in sandbox? You said that you have checked ST22 for authorization errors. ST22 ir for short dumps, not authorization errors, and since the workflow has clearly went into an error state, I don't think there are short dumps...
Kind regards,
Karri