Reproduction steps:
1. Open the user's attached project
2. In the Hierarchy find "boombox r1" -> "boombox paulo's", double-click on it to center it
3. In the Inspector window find Skinned Mesh Renderer -> BlendShapes -> "Wobble 2"
4. Slide "Wobble 2" slider to the right

Expected result: Editor continues working
Actual result: Editor freezes while looking at the boombox

Reproducible with: 2018.3.0b1, 2018.3.0b9, 2019.1.0a7
Could not test on earlier versions due to crashes while importing or missing prefabs from the scene

Note 1: Freeze doesn't occur on OpenGLCore
Note 2: It appears that the UI freezes graphically, not functionally, because it's possible to pan away from the boombox to unfreeze everything