Reproduction steps:
1. Open the attached user's project "OnPostRenderBug.zip"
2. In the Project window under "Assets/Scenes" open "SampleScene.unity"
3. Enable Quality Settings Anti Aliasing (e.g. 4x) in the Project Settings and enable Camera’s MSAA
4. Build the project on an Android device and enter Play Mode in the Editor to compare results (Editor: Post-Process is not shown while Anti Aliasing is, Android device: Anti Aliasing is not shown while Post-Process is)

Expected result: both the Editor and Android Player behave in the same way and the Post-Process effect is shown along with Anti Aliasing
Actual result: on Android devices the Post-Process is shown while Anti Aliasing isn't (See attached Android_Results.png)

Reproduces on: 2018.4.27f1, 2019.4.10f1, 2020.1.5f1, 2020.2.0b2

Reproduces with these devices:
OpenGLES 3 and OpenGLES 2:
N/A, Samsung Galaxy S9 (SM-G960F), Android 8.0.0, CPU: Exynos 9 Series 9810, GPU: Mali-G72
VLNQA00313, Huawei Y6 Ⅱ Compact (HUAWEI LYO-L01), Android 5.1, CPU: MediaTek MT6735, GPU: Mali-T720
VLNQA00316, Samsung Galaxy Note10 (SM-N970F), Android 9, CPU: Exynos 9 Series 9825, GPU: Mali-G76
Vulkan:
N/A, Samsung Galaxy S9 (SM-G960F), Android 8.0.0, CPU: Exynos 9 Series 9810, GPU: Mali-G72
VLNQA00316, Samsung Galaxy Note10 (SM-N970F), Android 9, CPU: Exynos 9 Series 9825, GPU: Mali-G76
Metal:
VLNQA00310 iPad Pro 12.9 1st gen (iOS 13.4.1)

Notes:
-The Post-Process effect is a Greyscale overlay
-The user's attached project has a workaround, to use it, uncomment the "#define WORKAROUND" directive in "PostProcessTest.cs"
-To verify easily if the Anti Aliasing is working on the device, use the accessibility feature to magnify a region
-To disable Anti Aliasing when in Play Mode in the Editor, keep the spacebar pressed
-On 2020.2.0b2 I cannot verify if Anti Aliasing is enabled because the App crashes when the accessibility feature to magnify a region is enabled
-Issue reproduces with Standalone Player as well