Description:

Since 5.5, Cubemaps baked by Reflection Probes are not readable with GetPixels/SetPixels operations anymore. They were automatically converted to the BC6H Format and cannot be read with the expected result.

To reproduce:

1. Open "Window/Cubemap Read Repro", a new Window should open.
2. Drag and drop "Uniy 5.5 Automatic (BC6H) (Error!)" Cubemap from the "Assets/Cubemaps" Folder into the Object Field of the opened Window.
3. Press "Read Cubemap" Button.

Result: False output in the Preview Texture underneath the button.
Picture attached to this letter.

5. Go back to Assets/Cubemaps Folder and Drag & Drop either Legacy or Unity 5.4 Cubemap on the Slot, press Read Cubemap Button again. Note these Cubemaps work as expected.

Note: Manually overriding the Texture Format of the BC6H Cubemap to use the RGBA32 Format works as expected (see the 5.4 Cubemap Example in Assets/Cubemaps).

Reproduces with: 5.5.0p3; 5.6.0b3;
Can't test with 5.4.0, some functions can't be found.