Poor RF performance on quick test

I am seeing very poor RF performance on the loopback test that is part of the quick test guide.
There seems to be a lot of noise and distortion as can be seen in the attached screenshot of the FFT Viewer.

I am running the latest version of LimeStudio. I did have to revert the firmware back from v16 to v12 because of this issue: ERROR: SetPllFrequency: error configuring phase