Steps to reproduce:
1. Open the attached repro project
2. Open the CornellBox scene
3. Bake the lighting using the Lighting window
4. Notice that the reflection probes appears dark in the inspector
5. Bake the reflection probes through its inspector view
6. Notice that it's now as it should be
(NOTE: the issue also goes away if you select non-directional mode in the lighting panel)

Observed on trunk revision b4a52c80b8a0

Repro project: https://drive.google.com/file/d/1uLWMILo0un_QrKG6M2NBB9-DA73sgxRh/view?usp=sharing

Reproduces on:
2021.2.0a1
2021.2.0a2
2021.2.0a3
2021.2.0a4

Does not reproduce on:
2021.1.0a5
2021.1.0b1
2021.1.0b2
2021.1.0b3
2021.1.0b4
2021.1.0b5

Reproduces with the CPU and GPU PLMs
Reproduced on BiRP, HDRP
Reproduced on Windows and macOS