Reproduction steps:
1. Open the attached user's project "AddressableVersionControlIssue.zip"
2. In the Project window select the "Asset/Data/PrefabList.asset" Scriptable Object
3. In the Top Menu select "File/Save Project"

Expected result: Saving a project which contains a ScriptableObject with an AssetReferenceGameObject list does not freeze the Editor for a short time
Actual result: Saving a project which contains a ScriptableObject with an AssetReferenceGameObject list freezes the Editor for a short time (See attached AddressablesIssue.mp4)

Reproduces on: Addressables 1.8.3, Addressables 1.11.2 (2018.4.25f1, 2019.4.4f1, 2020.1.0b16, 2020.2.0a18)
Does not reproduce on: Addressables 1.7.5 (2018.4.25f1, 2019.4.4f1, 2020.1.0b16, 2020.2.0a18)

Notes:
- Issue occurs only If you select the "PrefabList.asset". Subsequent saves of the Project will not have this behavior unless you reselect "PrefabList.asset"
- Issue is more obvious when connected to the Plastic SCM Plugin but the behavior can still be seen using Visible Meta Files as you can see the mouse cursor alternating between the regular cursor and the spinning progress wheel for every Prefab saved
- On 2020.2 the freeze is shorter than in 2020.1