Avid 2018.12.1. Continuum 2019. Mac OSX High Sierra. After adding Pan and Zoom to a clip, if I turn on Motion Blur it results in a BFX Error 25. Turning off Motion Blur clears the error
That was a bug introduced in 12.0.0 as part of an optimization. We already have a fix for it internally and it will be a part of the 12.0.1 update that will be released soon.
Sorry for the inconvenience!
The fix for this was released in Continuum 12.0.1. Any version higher than that should be fine.