How to reproduce:
1. Open the attached "1238629 repro" project
2. Select "Art.png" from the Assets folder
3. Right-click it and select "Reimport"
4. Repeat step 3

Expected result: the Asset is reimported without any errors
Actual result: 20 "Assertion failed on expression" errors are thrown

Reproducible with: 2020.1.0a23, 2020,1,0b10, 2020.2.0a1, 2020.2.0a11
Not reproducible with: 2020.1.0a15, 2020.1.0a22, 2020.2.0a12
Could not test with: 2020.1.0a14 and earlier (Sprite Atlas V2 isn't present)

Notes:
-Testing this with Unity Accelerator as a Global Cache (since Cache Server support is one the Sprite Atlas V2 features) caused a seemingly infinite AssetDatabase.ImportAssets loading pop-up
-This issue ussualy reproduces on every second reimport but very rarely only one reimport is required
-The errors state: Assertion failed on expression: 'ins.second || ins.first->second == artifactID || (ins.first->second == CircularDependencyArtifactID() && !artifactID.IsValid()) || GetPathFromAssetGuidV2(key.GetGUID()).ends_with(".cs")'
UnityEditor.TextureImporterInspector:OnDisable ()