Known Issue:
Instances where mongoose-unique-validator npm package causes incorrect error thrown involving _id must be unique error. It is an ongoing issue in mongoose-unique-validator npm package.
Affects
It affects frontend integration where bad requests status code 400 would be shown for adding or editing software as it will shown software as not added successfully.
Potential Workaround:
- To remove the 
mongoose-unique-validator plugin entirely and check the error code thrown by mongoose manually.
or 
- To wait for a bug fix in 
mongoose-unique-validator plugin. 
The stopgap measure:
Related Issue:
mongoose-unique-validator GitHub
GitHub Issue 1
GitHub Issue 2