1. What happened
On 5.3.2p4 it takes about twice the time to bake reflection and custom probes as in 5.2.4p1.

2. How we can reproduce it using the example you attached
For reflection probes (do for every version of interest):
- Open BakedReflectionProbeBakeTime scene
- Select main manu item: Bake > Reflection Probes
- Observe Console output

For custom reflection probes (do for every version of interest):
- Open CustomReflectionProbeBakeTime scene
- Select main manu item: Bake > Custom Probe
- Observe Console output

Note: this project is based on CustomReflectionProbeBakeTime and BakedReflectionProbeBakeTime performance tests.