Reproduction steps:
1. Open the "Assets/InitScene" Scene in the attached "case_1237323_package_mods.zip" project
2. Ensure that Use Multithreading is enabled (Edit -> Project Settings -> Physics 2D -> Job Options (Experimental) -> Use Multithreading)
3. Enter Play Mode
4. Observe the Editor's memory usage in Task Manager/System Monitor/Profiler

Actual result: Gradual increase in memory usage when compared to entering Play Mode without using multithreading

Reproduces on: 2019.3.11f1, 2020.1.0b6, 2020.2.0a9
Could not test with: 2017.4.40f1, 2018.4.22f1 - (Unable to strip the project enough to be able to downgrade and to run without compilation errors)

Developer's Note:
- Reduce the number of "Visitors" being spawned in the park from 1000 as that takes a long time to spawn. I reduced it to 100-200 as this clearly demonstrates the leak. Do this by selecting "Park1 > VisitorSpawner" GameObject. In the "Visitor Spawner" script, change the "Max Population" field.