Steps to reproduce:
1. Create a new project
2. Import "The Heretic: Digital Human" asset from the Asset Store
3. Using Package Manager, install FBX Exporter package
4. In Project Window right-click on "Gawain_DemoVariant.prefab"
5. Select "Convert To FBX Linked Prefab..."
6. Click "Convert" in the Convert Window

Expected result: Unity doesn't lockup focus on itself at some point of exporting
Actual result: Unity locks up focus on itself at some point of exporting, rendering the computer almost unusable for a bit of time

Reproducible with: FBX Exporter 2.0.2-preview.1, 3.2.0-preview.2 (2019.3.16f1, 2019.4.1f1, 2020.1.0b13, 2020.2.0a15)
Couldn't test 2.0.1-preview.2 due to Timeline namespace missing errors, couldn't test up to 2.0.1-preview.11 due to no "Convert To FBX Linked Prefab..." option

Notes:
- The lockup happens after "Importing Assets" finishes
- It reproduces both when Unity is focused at the time and if the focus is on another program, which creates work stops
- On Windows Unity just freezes, but doesn't lockup focus