How to reproduce:
1. Open the attached project "1203634.zip"
2. Open the Sample Scene
3. Open the Profiler window (Window -> Analysis -> Profiler)
4. Enter Play mode
5. Select any frame in the Profiler

Expected result: There is no GC Alloc under GUI.Repaint
Actual result: There is 1.1 KB of GC Alloc under GUI.Repaint every frame

Reproducible with: Unity 2018.4.14f1 (3.0.1, 3.3.1), Unity 2020.1.0a16 (3.0.1, 3.3.1)

Notes:
It does not matter if Monetization.Initialize is called once or multiple times, there will always be 1.1 KB of GC Alloc every frame.
UnityEngine.Monetization did not exist prior to package version 3.0.1, therefore the issue was not reproducible.