Hi @proudgis, the ListExploder will not reject nested lists. Depending on your FME version, rejected features might have an attribute called "fme_rejection_code" which stores a string describing the reason for the rejection. Did you check this?

Thanks for the reply @takashi, I do have the 'fme_rejection_code' and the string upon failure is 'MISSING_PARAMETER_LIST'. I can't seem to figure out why this is occuring as this transformer is set-up just like other ListExploders before it.

Try inserting a breakpoint or an inspector just before the ListExploder and verify that the list really exists on your features when executing your workspace.

The rejection code appears when the feature does not have the list or the first element (i.e. index=0) of the list is missing. As David suggested, check whether the feature has the list (and it has the first element).

Perhaps that is the issue here, however how can I generate a dynamic FMW if sometimes the data is there and sometimes not?

Use a tester prior to the list exploder to check for the existence of the list. If it's not there, what do you want to do with the feature, assign a default value and then continue processing or route it for special processing, or terminate the translation?