Reproduction steps:

1. Open the attached project;
2. Open the scene 'TestScene';
3. Create an empty gameobject;
4. Drag 'NavMeshAgentTest' or 'OffMeshLinkTest' script to the created object;

Actual result: the script appears in a gameobject, however required component does not appear.
Expected result: the required component should appear in a gameobject.

Reproduced with: 5.5.0f3, 5.6.0b1
Not reproducible: 5.4.3f1

Fixed in 5.6.0b3