To reproduce:
1. Open attached project “zProject_541034.zip”
2. Open “Scene.unity” scene and build for iOS device
3. Deploy the project to iOS device
4. In Xcode navigate to on the left side Show the Debug navigator tab and select Memory
5. On iOS device press the buttons multiple times and observe as after every press of the button memory is not cleared and keeps stacking up

Expected result: memory is cleared after a button is pressed
Actual result: memory is not cleared and keeps stacking until device runs out of memory and crashes

Reproduced on:
2017.4.11f1 2018.1.9f2 2018.2.7f1 2018.3.0b1

Device reproduced on:
iPhone 7 Plus iOS 11.1
Also reproduced on Editor on iMac MacOS 10.13.5
Windows 10 machine
Google Pixel 2 XL Android: 8.1.0 Snapdragon 835 MSM8998 Adreno (TM) 540 OpenGL ES 3.2 710KPZK0465061

Notes:
on 2018.3.0b1 the memory is increasing more slowly, step by step (1830b1.png)
Buttons are using: UrlTextureLoader urlTextureLoader = gameObject.AddComponent<UrlTextureLoader>();