Reproduction steps:
1. Open the attached project "case_1217903-ReimportAllNativePlugin.zip"
2. In the Project window right-click to open the context menu and click "Reimport All"

Expected result: referencing the DLL by [DllImport("ReimportAllNativeLibrary")] should yield the same result as [DllImport("Assets/Plugins/Editor/native/ReimportAllNativeLibrary")]
Actual result: DLL exception is thrown in the console window

Reproduces on: 2019.1.8f1, 2019.3.3f1, 2020.1.0a24
Does not reproduce on: 2017.4.37f1, 2018.4.17f1, 2019.1.7f1

Notes:
-This problem does not occur when directly referencing the dll within the project
-When using [DllImport("Assets/Plugins/Editor/native/ReimportAllNativeLibrary")] works as expected but is not dependable as the directory can be moved into "Assets/3rd Party/MyStuff"
-Issue does not reproduce on Windows 10 with 2019.1.7f1 and below
-On macOS reproduces with 2017.4, 2018.4, 2019.3, 2020.1