Reproduction steps:
1) Open any project - can be empty.
2) Open up Edit > Project Settings > Editor
3) In upper right of an Inspector hit triangle located on a side of a gear.
4) Hit reset.

>Expected result: All Editor Settings values are reset to their defaults.
>Actual result: Components disappear from Editor Settings and an IndexOutOfRangeException can be seen in the console.

Workaround: Minimizing and bringing unity back up will fix missing components.

Regression introduced in: 5.4.0a6