Steps to reproduce:
1. Open user's attached project in "case_1293458-VulkanUnableToUnloadGraphicsMemory.zip"
2. Enable development build (File -> Build settings)
3. Build for iOS and open the project in Xcode
4. Go Product -> Scheme -> Edit scheme
5. Under Diagnostics enable Metal API validation
6. Under options set GPU Frame Capture to Metal
7. Deploy the project to a Device
8. Capture GPU Frame and inspect the Memory
9. Resume the application, Switch to Scene2, and then Scene1 again
10. Capture GPU Frame and inspect the Memory (read note 2)

Expected results: Memory usage will be the same as in step 8
Actual results: Memory usage is increased, bound unused Shadowmap and UnityAttenuation are visible in the memory

Reproduces on: 2019.4.17f1, 2020.1.17f1, 2020.2.0f1, 2021.1.0a10
Could not test: 2018.4.30f1 (due to project breaking)

Reproducible with these devices:
iPad Pro 12.9 1st gen (13.4.1)
iPhone 6S (iOS 13.3.1)
iPhone 12 Pro (iOS 14.2.1)

Notes:
1. Screenshots are attached
2. This can be tested by inspecting the RAM and without capturing the GPU frame. The RAM will have increased after switching back from the second scene to the first compared to when the app was first launched (~50MB)