I have a test scene for a hi-res terrain with RTP etc. Not much else in the scene at all.
The editor crashed suddenly; I believe the last change was to remove a deprecated substance texture from a surface before saving the scene, because it kept throwing error messages/assertion errors on flags - in the console.

To reproduce:
1. Open attached project
2. Open scene
3. Editor crashes

Reproducible: 5.5.0b8, 5.4.2f1, 5.3.6p7