To Reproduce:
- Open repro.unity scene
- Press play
- Reimport a script from project view
- observe Console output

ClassA,ClassB and ClassC have ScriptExecutionOrder defined.

On Playmode:
OnEnable ClassA Obj[x]
OnEnable ClassA Obj[y]
OnEnable ClassA Obj[z]
OnEnable ClassB Obj[x]
OnEnable ClassB Obj[y]
OnEnable ClassB Obj[z]
OnEnable ClassC Obj[x]
OnEnable ClassC Obj[y]
OnEnable ClassC Obj[z]

After reimport, classes do not execute in order shown in ScriptExecution order, or even one type after another, an example:
OnEnable ClassB Obj3
OnEnable ClassA Obj3
OnEnable ClassA Obj1
OnEnable ClassC Obj3
OnEnable ClassC Obj2
OnEnable ClassB Obj1
OnEnable ClassC Obj1
OnEnable ClassB Obj2
OnEnable ClassA Obj2

Expect to see OnEnabled called in the same type order as entering playmode for classes with discrete ScriptExecutionOrder.

Reproducible: 2018.3.0a1, 2018.2.0b13, 2018.1.0f2, 2017.1.1p3