Repro:
1. Sync the repro project at the revision listed above. Open and import the project
2. Open the Scene MultiBounce_WIP01
3. Ensure Progressive Updates are OFF and Auto Generate is OFF
4. Set the lightmapper to Progressive GPU and choose sample counts 1000, 1000, 1000
5. Set the lightmap resolution to 60 texels, which will necessitate using 7x1024 lightmap sets
6. Generate Lighting
7. While the bake is running, select the Light "DoorForeground_Area"
8. Adjust the colour of the light. This will cause the bake to restart.

Observe:
Using GPUZ to track, watch the memory usage during the bake. In the test Scene using the settings above, we're using around 5.5GB of video memory for Windows+Editor+Bake. When the Light is modified, dirtying the Scene, the bake will restart. For a brief moment, memory usage will spike to around 11GB. If this exceeds the available video memory, this will cause the lightmapper to fallback to CPU with the errors:

OpenCL Error. Falling back to CPU lightmapper. Error callback from context: CL_MEM_OBJECT_ALLOCATION_FAILURE error executing CL_COMMAND_NDRANGE_KERNEL on TITAN V (Device 0).

OpenCL Error. Falling back to CPU lightmapper. Error callback from context: CL_MEM_OBJECT_ALLOCATION_FAILURE

Expected:
There should not be any large spikes in video memory caused by restarting the bake.