Change the GI Cache Setting in preferences.

To add: the question only occasionally comes up in Mobile,but always comes up in
Editor.(┙>∧<)┙へ┻┻

To add: the question only occasionally comes up in 5.6.3f1, and I'm trying to determine if my code is wrong

Same problem in Unity5.6.3 f1
Oh~~~It's been over a year and a half
Can someone tell me how to solve this problem?

I've found that if you open the lighting option found in the Window menu there is a place for skybox and sun(light source). simply apply your light source for the scene in the sun field and your skybox, I used the default one, in the skybox field and then select build from the same window. Fixed it for me. Hope this helps

5.3.2p2 user here, still can confirm warning appearing:

Lightmap snapshot 'LightmapSnapshot' is inconsistent - 2 files out of 8 are missing. Realtime GI will be disabled. Please rebuild lighting for this scene.
UnityEditor.DockArea:OnGUI()

Note that this is a project migrated from 5.2.0, and slowly migrated incrementally upwards (including patch updates) to 5.3.2p2.

This is still an issue in 5.3.2f1. Are you saying that you need to relightmap? Also, your saying that this is caused by more than one machine opening the project? What if you have a VM for windows so you can build all platforms?

This is still an issue in 5.3.2f1. Are you saying that you need to relightmap? Also, your saying that this is caused by more than one machine opening the project? What if you have a VM for windows so you can build all platforms?

I still have this issue... Are you saying that what causes this is if another machine opens the project? What if you have a mac and parallels VM (need both to build all platforms)?

5.3.1f1 still has this issue.

Failed opening GI file: '3f/3f3fd667d0e34dd477e6f50c8cd252df.rpc.sse'.
Failed loading probe set data for hash: 0x3f3fd667d0e34dd477e6f50c8cd252df
Error adding system: Data not available.

The last error is a new one in 5.3.1.