How to reproduce:
1. Open the attached "1260054 repro" project
2. Open the "FBXCleaner.cs" Script from the Assets > Editor folder
3. Uncomment code from line 30 to line 42 inside the "FBXCleaner.cs"
4. Select the "claw_hand3.fbx" Asset from the Assets folder
5. Right-click it and select Reimport

Expected results: the Project window content is refreshed and updated
Actual results: the Project window doesn't update and shows the deleted Assets

Reproducible with: 2019.4.3f1 (Asset Import Pipeline V2), 2020.1.0b14, 2020.2.0a4
Not reproducible with: 2019.4.3f1 (Asset Import PipelineV1), 2020.2.0a5, 2020.2.0a16
Could not test with: 2018.4.24f1 (Asset Import Pipeline V2 isn't available)

Notes:
-This issue also reproduces with .obj and .dae file formats
-This issue doesn't reproduce with Asset Import Pipeline V1
-Triggering a Domain Reload, restarting the Editor or selecting Reimport All solves the issue
-The issue doesn't reproduce if the Script is fully uncommented when opening the project or importing a new model, it seems to only reproduce when the model is already present in the project at the time of introducing the post-processing