TFS Test and Build report back as Failed despite 100% tests passed

From my on-premises TFS 2018 I get the following report back:

How can a test be failed an yet 100% passed?

If I look at the detailed error message it tell me that all steps except for 64 bit tests was successful.

I'm at a bit of a loss how to troubleshoot here - Only error I have in the log is this error:

2017-12-14T03:52:18.5302240Z ##[error]An exception occurred while invoking executor 'executor://mstestadapter/v2': Error while unloading appdomain. (Exception from HRESULT: 0x80131015)