Just pointing out that I had a similar log on my build and I got it solved:
I'm running a local Jenkins server in Windows with a unique constructor on it, so no interactions with Jenkins slaves. My workspace was configure to output .trx on a hardcoded file path (something like 'C:\TestResults\') which was different from job's workspace.
Looks like Jenkins can't access hardcoded paths, which is certainly a security measure to avoid access to system directories.
The solution was use WORKSPACE placeholder variable to set in execution script (which was a command prompt) and setting plugin's TRX path to */.trx (which is every .trx file in job's workspace). That solved the problem.