Switching to SM4 when you have LPVs active in a project will crash a project.
Also reproduced in Main Promotable-CL-2589716 and 4.8.0 Launcher
RESULTS: Brief Pause then Crash
EXPECTED: Either a Warning that SM4 is unavailable or like Distance Fields, it reverts back to not using LPVs.
Head over to the existing Questions & Answers thread and let us know what's up.