From UDN:
https://udn.unrealengine.com/s/question/0D54z00009aITCaCAO/material-editor-crash-on-parameter-name-that-is-shared-in-material-function?fromCase=1
- Create a new material and add a scalar parameter named A.
- Create a new material function and add a scalar param named A (same name as in the material).
- Place the created material function in the material.
- Change param A's value.
Effect: Regardless whether it's plugged or not, the material editor will crash upon changing the value of the parameter.