How to reproduce:
1. Open the "SampleScene" in the attached project "case_1174195-SSR_Bug"
2. Make sure SSR is enabled in the "Post-Process Volume" GameObject
3. In the Main Camera Inspector, set the HDR to "off"

Expected results: No errors are thrown
Actual results: CopyTexture() errors are thrown

Reproducible with: 2018.4.6f1, 2019.1.14f1, 2019.2.1f1, 2019.3.0a11 (Package ver. 2.1.6, 2.1.7)
Not reproducible with: 2017.4.31f1 (using Post Processing Stack from Asset Store)

Additional notes:
1. Full error message:
"Graphics.CopyTexture can only copy between same texture format groups (d3d11 base formats: src=27 dst=9)"

2. With Post Processing version 2.1.5 and lower no errors are thrown, but the Game window is a black screen. However, Enabling "Directly to Camera Target" checkbox in the "Post Process Layer" Component of the Main Camera fixes the black screen problem.

3. On several Unity versions, different errors occur. For example, in 2019.2.1f1 (package ver. 2.1.7) such error is thrown:
"RenderTexture.Create failed: format unsupported for random writes - RGBA8 sRGB (4).UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)"

4. Post Processing Stack Asset was throwing an error in Unity 2018.4. Full error message:
Assets\PostProcessing\Editor\PropertyDrawers\MinDrawer.cs(6,34): error CS0104: 'MinAttribute' is an ambiguous reference between 'UnityEngine.PostProcessing.MinAttribute' and 'UnityEngine.MinAttribute'