Steps to repro:
1. Download the attached project and open "tree" scene;
2. In the Lighting window (Window>Rendering>Lighting) press Generate Lighting button.

Expected result:
GI baking proceeds and finishes as expected.

Actual result:
GI baking stalls on "Baking..." stage. See attached screenshot.

Notes:
- Reproducible in Version 2021.2.0a9, 2021.1.0f1, 2020.3.1f1, 2019.4.22f1;
- Reproducible on Windows;
- Branch lighting/fix-uv-bounds-calculation seems to have addressed unrelated speedtree lightmap UV non-finite errors also stalling tha bake ("Line 229 in Wintermute::Geometry::Verify - Geometry geom a586ce87f2b8e1ed6d08959bed50579b: 2860632 components out of 28606320 total are non-finite")
happening with the same project and steps (described in the case 1319133), however, this issue seems to be different from the one reported in the case 1319133. The logs obtained in trunk and in lighting/fix-uv-bounds-calculation (which is gonna be merged with trunk soon) seem to be different. See attached logs, please;
- In the trunk's Version 2021.2.0a9 (5be3997fdbde) the baking stalls on "Preparing Bake..." stage, in the lighting/fix-uv-bounds-calculation branch (b69268c7977b) the baking stalls on "Baking..." stage. See attached logs from both branches, please.
- The baking stall is reproducible when baking GI either with Progressive CPU, GPU Lightmappers and Enlighten;
- Clearing cache, baked data or restarting Editor doesn't seems to fix this bug;
- Disabling SpeedTree gameobject fixes the issue.