To reproduce:
1) Open attached project
2) Open two inspector tabs
3) Find a random sprite/image in project view (for example, ArenaBackground)
4) Click it to make it appear in inspector
5) Lock one of the inspectors
6) Open Player Settings -> Splash Screen
7) Remove Unity Logo and add your selected sprite/image for 10 seconds
8) Click "Preview"
9) While it is still previewing, change the sprite's/image's 'Max Size' in locked inspector and apply
10) Editor crashes

Reproduced in 5.5.0b4 5.5.0b8, 5.5.0f3, 5.5.0p1, 5.6.0a6