Steps to repro:
1. Download the attached repro project (from the comments section);
2. Open 'Spotlight_Tunnel_PLM' scene;
3. Open the Preferences window (Edit-Preferences...);
4. In the Preferences window open GI Cache tab;
5. With the GI cache tab opened navigate in the Scene view (scroll, pan, zoom).

OR

1. Create new project with 3D template;
2. Add cube gameobject;
3. Mark the cube gameobject as lightmap static (Contribute GI);
4. Switch the Directional light type to Baked;
5. Bake the scene's GI;
6. Open the Preferences window (Edit->Preferences...);
7. In the Preferences window open GI Cache tab;
8. With the GI cache tab opened navigate in the Scene view (scroll, pan, zoom).

OR

1. Create new project with either LW or HDRP template;
2. Open the Preferences window (Edit->Preferences...);
3. In the Preferences window open GI Cache tab;
4. With the GI cache tab opened navigate in the Scene view (scroll, pan, zoom).

Actual result:
Editor is almost unresponsive and extremely slow. It looks like some assets are being imported/updated in the background. See attached video and Editor.log.
Regression introduced in Version 2019.2.0a12.

Expected result:
Editor performance is stable and consistent regardless of whether the GI Cache tab is opened or not.

Notes:
- Reproducible in 2019.3.0a1, 2019.2.0a13, 2019.2.0a12;
- Not reproducible in 2019.1.0f2, 2019.2.0a11;
- Reproducible on Windows 10 and OSX 10.14.4;
- Reproducible on Legacy, HDRP and LWRP;
- Reprodicible in HDRP and LWRP versions 5.2.3;
- Reproducible only when the GI Cache tab is active, not reproducible when other tabs of the Preferences window are active;
- The issue gets even more severe when GI Cache tab is active when baking - the Editor is completely unresponsive in this case.