What are these differences in two DLL file generated from the same source code

This might have something to do with differences between Build and a ReBuild

Difference between Build Solution, Rebuild Solution, and Clean Solution in Visual Studio?

if it doesn't think it needs to rebuild a project, it won't. It may also use partially-built bits of the project if they haven't changed

Performing a build uses metadata behind the scenes and thus your dll's can be different

Why is a different dll produced after a clean build, with no code changes?

SOLUTION:

You will need to perform a deterministic build as described here