Some time ago we switched to NUnit 3.12 and NUnit3TestAdapter in Camlex library and noticed the following problem with ReSharper unit test runner: all unit tests were marked as “inconclusive” and didn’t run. At the same time built-in Visual Studio test runner worked. I used 2019 version of ReSharper when found this problem.
By searching the web I found similar problems from other people in JetBrains support site. In order to fix it I uninstalled 2019 version and installed latest available version of ReSharper JetBrains.ReSharperUltimate.2020.1.3. After that test become working again:
So if you will face with the same problem try to install last ReSharper version.