The input PDF ha incorrect tag structure' while trying to merge files

Hi to all.
I have to merge a set of PDF uploaded by users on which ( unfortunately ) i have no control.

Most of the times everything goes well and the result pdf is created, however sometimes the API returns this error

com.adobe.pdfservices.operation.exception.ServiceApiException: description ='The input PDF has incorrect tag structure.; transactionId=RMDbanAHeOG8gh8DfTf9Bg43q95DGdIu'; requestTrackingId='XG4umpNiSkudFNiDkWm8DNI8DiTDLaPP'; statusCode=400; errorCode=INVALID_PDF_TAGGING

Is there a way to avoid this exception or at least know which of the files that should be merged provokes it ?

Thank you for your answer!