Reproduction steps:
1. Open the user's attached project "TEST_BUG_fpS.zip"
2. In the Project window under "Assets/Scenes" open "SampleScene.unity"
3. In the Build Settings, switch the platform to Standalone for the GameObjects to appear
4. Switch the platform to Android or iOS for the GameObjects to disappear

Expected result: RenderTexture does not stop rendering GameObjects when switching platforms if Clear Flags Skybox option is selected
Actual result: RenderTexture stops rendering GameObjects when switching platforms if Clear Flags Skybox option is selected

Reproduces on: 2017.4.38f1, 2018.4.19f1, 2019.3.6f1, 2020.1.0b2, 2020.2.0a4

Tested on these devices:
VLNQA00033, Samsung Galaxy Nexus (Galaxy Nexus), Android 4.3, CPU: TI OMAP 4460, GPU: PowerVR SGX 540
VLNQA00122, Samsung Galaxy S9 (SM-G960F), Android 9, 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
VLNQA00038, Htc Desire 510 (HTC Desire 510), Android 4.4.3, CPU: Snapdragon 410 MSM8916, GPU: Adreno (TM) 306
VLNQA00277, Asus ROG Phone (ASUS_Z01QD), Android 8.1.0, CPU: Snapdragon 845 SDM845, GPU: Adreno (TM) 630

Notes:
-Does not reproduce on a New Project
-Reproduces on Vulkan, OpenGLES3
-This issue can be rarely accompanied by visual artifacts on the RenderTexture
-Changing the second Camera Clear Flags to Solid Color produces inaccurate rendering of GameObjects