How to reproduce:
1. Create a new Unity project
2. Import the tester-attached package(TerrainCluster.unitypackage)
3. Turn off Auto Generate in the Lighting Settings window
4. Add the Prefab TerrainCluster to the Scene
5. Set the Lighting Generation Lightmapper to 'Progressive GPU (Preview)'
6. Generate Lighting

Expected result: the Lightmapper does not fall back to CPU Lightmapper and no crash occurs

Actual result: Editor crashes with the following stack trace:
Thread 0x70000444f000 may have been prematurely finalized
#0 0x00000114b4a9c6 in RadeonRays::PlainBvhTranslator::Process(RadeonRays::Bvh&)
Thread 0x70000444f000 may have been prematurely finalized
#1 0x00000114b475d4 in RadeonRays::IntersectorSkipLinks::Process(RadeonRays::World const&)

Crash(macOS Radeon Pro 580 8GB):
Reproducible with: 2020.1.0a5, 2020.1.0a14
Not reproducible with: 2019.2.14f1, 2019.3.0f1, 2020.1.0a4
Could not test with: 2017.4.35f1, 2018.4.13f1(GPU lightmapper unavailable)

Stacktrace from 2020.1a18:
#0 0x00000114b4a9c6 in RadeonRays::PlainBvhTranslator::Process(RadeonRays::Bvh&)
Thread 0x70000444f000 may have been prematurely finalized
#1 0x00000114b475d4 in RadeonRays::IntersectorSkipLinks::Process(RadeonRays::World const&)
Thread 0x70000444f000 may have been prematurely finalized
#2 0x00000114b37dcc in RadeonRays::CalcIntersectionDevice::Preprocess(RadeonRays::World const&)
Thread 0x70000444f000 may have been prematurely finalized
#3 0x00000114b36bcc in RadeonRays::IntersectionApiImpl::Commit()
Thread 0x70000444f000 may have been prematurely finalized
#4 0x0000010c606207 in RadeonRaysMeshManager::StoreToGPU(OpenCLState&, OpenCLCommonBuffers const&)
Thread 0x70000444f000 may have been prematurely finalized
#5 0x0000010c627820 in RadeonRaysBakeLightmapTechnique::AttachHeavyDataPointers(int, int, RectT<float> const&, int, RefcountedDataHandle<PVRGBufferHeavyData> const&, RefcountedDataHandle<PVRLightmapBakeHeavyData> const&)
Thread 0x70000444f000 may have been prematurely finalized
#6 0x0000010c5bc725 in BakeJobInitializeLightmapData::Execute(bool*)
Thread 0x70000444f000 may have been prematurely finalized
#7 0x0000010c572529 in BakeContextManager::UpdateFunction()
Thread 0x70000444f000 may have been prematurely finalized
#8 0x0000010c5722a9 in BakeContextManager::UpdateFunctionDispatcher(void*)
Thread 0x70000444f000 may have been prematurely finalized
#9 0x00000109bed3cc in Thread::RunThreadWrapper(void*)
Thread 0x70000444f000 may have been prematurely finalized
#10 0x007fff6496fe65 in _pthread_start
Thread 0x70000444f000 may have been prematurely finalized
#11 0x007fff6496b83b in thread_start

Notes:
Crash reproduced on macOS Catalina 10.15.1 with Radeon Pro 580 8GB
Crash did not reproduce on Windows 10 with GTX 1060 6GB