subworkflow completed but main workflow not going further

Hi All, 

I am calling an approval subworkflow from the main workflow for all the approvers using multiline element. Sometimes even if all the users have processed their workitems, main workflow did not continue. Enclosed the screenshot from the technical log.

As it is visible there were two approvers and the complete subworkflow for both the users have been completed but still the status of the subworkflow step is in process.

Please guide !

Thanks

LS