This issue had been observed in the past and was fixed in release 17.9 and i assume you would be on a build higher than that so could you please raise a support ticket for the same and our team can help you to fix the issue. Also provide them with details of the package that you are trying to import which will help them to reproduce the issue.
In my opinion error comes from a bad definition of the builtin cusResource schema which generates duplication error when importing a custom resource which is already in the DB .
This error means one of the component of the package which is present in the xml is missing on environment B. When you try to import the package and get the above mentioned error , I would suggest to review the web logs( Environment B) which would tell you about the error in detail and help you fix the same.
The package has only workflows, so no cusResources are involved (I could figure out the two workflows generating the error by importing the workflows one by one, but still not able to solve the problem)
I am using Adobe Campaign Standard (not Classic). Where can I find the web logs? The only log that I can find is in Administration> Development> Diagnosis> Batch jobs. It is showing what I have posted above with no further details. Thank you!