During the world optimization process, the game first upgrades all entity region files, then all point of interest region files and lastly all chunk region files. When switching to the last stage of the process, the progress bar's percentage and colors are not reset immediately, only changing to the actual value when they receive an update, like moving from 1% to 2%.

How to reproduce:

1. Find a large world from an older version of the game (not required, but it's easier to notice the issue this way).
2. Select the world, click "Edit" and then "Optimize World."
3. Choose either "Create Backup and Load" or "I know what I'm doing!".
4. Observe the progress bar as it switches to the chunk upgrading stage.

Expected result:

The percentage would immediately reset to 0% and all colored sections in the progress bar would be turned to black.

Observed result:

The percentage did not change and the colored sections remained, waiting to be updated as the optimization process makes progress.