I struggled with quite similar problems. In my case it was a problem with DP Packages folder and / or the Access Account on the package itself.
Can you check once the MANAGE ACCESS ACCOUNTS on the package in your software library overview and do also a check on the permissions at the SMSPKGC$ . I do not know which account you are using for the task sequence to get the packages. If you did any changes do not forget to update distribution point.