To reproduce:
1) Create new project
2) Open Test Runner Window
3) Enable Playmode Tests (and restart editor when prompted)
4) Create Playmode Test
5) Create some dud Assert (like Assert.AreEqual(15,16))
6) Create new C# script
7) Reimport step 6 script
8) Quickly (while recompiling process is still going) Run All (or just that Playmode test)

Expected: All goes normally
Actual: TestRunner temp scene is created but then the process gets stuck and the tests aren't tested

Reproduced in 5.6.3p3, 2017.3.0b4