To reproduce:

1. Download attached "1172619_repro.zip" project in Unity
2. In Project window select "untitled.fbx" gameObject
3. In Inspector press Materials button, to go to Model Importer Material Editor
4. In Material field press dot button
5. In opened window try to select "FrameDebuggerRenderTargetDisplay" Material
6. Observe that in the Material field this Material is shown
7. Try to select another Material

Expected results: Newly selected Material is shown in Material field
Actual results: "FrameDebuggerRenderTargetDisplay" Material is still shown in the Material field, no matter which Material you select

Notes:
- Video for Reference is attached
- If you close Material selection window and open it again, there will a lot of more Materials than previously
- If you try to select "Materials" which haven't been previously then Material field updates as "None (Material)" and again you cannot select new Material, but if you close that window and open it again, there will be only "Originals" Materials, as there was from the Start
- If you don't try to select "Materials" which haven't been previously then you can select all Materials and Material Field updates always, even after selecting "FrameDebuggerRenderTargetDisplay" Material
- There is a lot of Materials in that Window which breaks Material Field and cause above mentioned issue, not just "FrameDebuggerRenderTargetDisplay" Material
- There is another issue but only on 2019.3.10f1 - if you Extract Material, Delete it and try to Extract it again, it throws you a Window in which you are asked are you wanna re-extract Material. No matter which choice you select, Console throws an Error:

"EndLayoutGroup: BeginLayoutGroup must be called first. UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr) (at /Users/builduser/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:187)"

Reproduced on Unity 2019.3.10f1, 2020.1.0b6 and 2020.2.0a7
Not reproduced on Unity 2019.3.9f1
Regression on Unity 2019.3.10f1