For me the editor crashes only if an actor with such material is selected with LPV enabled.
A workaround I’ve been using is setting the view mode to unlit (Lit=>Unlit on the third dropdown from left to right at the top of the viewport) before selecting the actor or material and making whatever changes I need. After that deselect the object and set the view mode to lit once again (Unlit => Lit).
Just be careful not to accidentally click on the actor after that, or else the editor will crash.
For your particular case (assuming the issue is the same):
- Enable LPV
- Bring an object with more than one material ID’s into the map
- Set view mode to Unlit
- Insert any translucent or additive material in any of the slots
- Deselect the actor
- Set view mode to Lit