Usually you will find the answer in the task log for that specific file. If the default logging folder was not changed, you will find them in C:\ProgramData\QlikTech\DistributionService\ (each QDS node has its own subfolder numbered 1, 2, 3, etc.. ) and then a subfolder with the date the task was run and then a further subfolder with the task starting timestamp and name.
Daniele - Principal Technical Support Engineer & SaaS Support Coordinator at Qlik If a post helps to resolve your issue, please accept it as a Solution.