Steps to reproduce:
1. Download attached project
2. Switch platform to UWP and build project
3. Open VS solution and build to HoloLens
4. Wait for 10 seconds
5. Check console

Results: Null exception is trigger when saving WorldAnchorStore.

ArgumentNullException: Value cannot be null.
Parameter name: _unity_self
at UnityEngine.XR.WSA.Persistence.WorldAnchorStore.Save (System.String id, UnityEngine.XR.WSA.WorldAnchor anchor) [0x00000] in <00000000000000000000000000000000>:0
at AnchorStoreReloader+<AddAnchorAfterloadoOmpleted>d__12.MoveNext () [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.MonoBehaviour.StartCoroutine_Auto (System.Collections.IEnumerator routine) [0x00000] in <00000000000000000000000000000000>:0
at AnchorStoreReloader.Update () [0x00000] in <00000000000000000000000000000000>:0
UnityEngine.MonoBehaviour:StartCoroutine_Auto(IEnumerator)
AnchorStoreReloader:Update()

Reproduced with: 2019.3.0a7, 2019.2.0b8, 2019.1.9f1, 2018.4.3f1

Note:
- reproducible with .NET and Il2CPP backends