Blueprint class's parents class reset to base class after restart engine

I create a blueprint class from a C++ class:

284088-qq截图20190804164024.jpg

after restart ue4 engine
blueprint’s parents class is Vehicle

284089-qq截图20190804164219.jpg

but after i open blueprint editor
blueprint’s parents class reset to WheelVehicle

284090-qq截图20190804164346.jpg

how can i fix it?
thanks for help!