I would expect a not authorised response rather than a request timeout if the token expired.
Adding the two parameters set at the max value for both resolved the issue. We set the values using set statements where MRC=15 and RTO=60
set Operation=-debug -service %ServiceUrl% -auth %AuthUrl% -workspace %WorkspaceId% -model %ModelId% -process "Update DH1" -chunksize %Chunksize% -file %FileName% -put %FilePath% -maxretrycount %MRC% -retrytimeout %RTO% -execute -output %DumpName%
Thanks @ben_speight @anirudh For your help, going to make the rest of my massive data loads stress free and hopefully failure free!