Repro:

1. Download and import the attached repro project into the Unity Editor shown above
2. Open the Scene PlanarReflectionBug.unity
3. Toggle off Lighting in the Scene View to use MatCap mode
4. Ensure that you are using high-enough sample counts in the Lighting Window for a reasonably long bake (for easier testing)
5. Hit Generate Lighting
6. While the bake is in progress, rotate and move the Scene View camera. Wiggle it. Just a little bit

Observe:
As the Scene View camera is moved, the GI bake will continually restart. This can be most easily seen by clicking the progress bar in the bottom right.

Expected:
Bakes should be unaffected by movement of the Scene View camera.

Notes:

I've tracked the issue down as occurring specifically when there is:

- A realtime reflection probe (planar or classic) in the Scene
- HDRP visual environment with ambient mode set to static
- A static lighting sky assigned in the Lighting window
- The matcap Scene view is being used (Scene View lighting toggle off)
- When all these things are true, it looks the the editor continually restarts any in-progress bakes on movement of the Scene View camera. The issue does not occur when the ambient mode is set to dynamic by the HDRP volume. My hunch is that HDRP is somehow dirtying the ambient probe.

Editor:

Version: 2020.1.0b4.3439
Revision: 2020.1/staging 7e2ed8c1221a
Built: Thu, 26 Mar 2020 00:59:05 GMT

HDRP:

8.0.1 also found in 9.0.0