Problems after update

One of my projects is running stable with grape-entity 0.3.0. But as soon I update to 0.4.0 or higher some of my tests fail. The odd thing is that they fail randomly and it seems that the connection to MongoDB randomly fails. I'm getting errors like this:

Problem:
   Document(s) not found for class Project with id(s) 555b4d484fe53d4ad2000310.
 Summary:
   When calling Project.find with an id or array of ids, each parameter must match a document in the database or this error will be raised. The search was for the id(s): 555b4d484fe53d4ad2000310 ... (1 total) and the following ids were not found: 555b4d484fe53d4ad2000310.
 Resolution:
   Search for an id that is in the database or set the Mongoid.raise_not_found_error configuration option to false, which will cause a nil to be returned instead of raising this error when searching for a single id, or only the matched documents when searching for multiples.

If I downgrade to 0.3.0 all tests are green again.

Any idea what could be the reason?

Reproduce the failing tests while comparing grape-entity 0.3.0 with 0.4.0 and later, focusing on the reported MongoDB lookup failures. No files or tests are named in the issue; done means identifying the version regression and restoring consistently passing tests.