When a vehicle is on an uneven surface, the physics that are handling where the wheels should be placed is resolving sporadically, causing noticeable jitters and sometimes flipping.
Regression?: Yes
This did not occur in 4.13.2-3172292+++UE4+Release-4.13
This does occur in 4.14.0-3195953+++UE4+Release-4.14
Head over to the existing Questions & Answers thread and let us know what's up.