Rebuilding index progress in progress bar does not match progress in log

Issue Summary

When rebuilding index, progress bar will show progress from UI.
However, the progress percentage in progress bar does not match progress in log at the same time.

This is reproducible on Data Center: (yes) 

Steps to Reproduce

1. Have a site with some spaces and pages. If the site has only small number of pages, reindex may finished too quick to show this issue. 
2. Open command console to monitor index log file (atlassian-confluence-index.log).
3. In Confluence site, move to  CONFLUENCE ADMINISTRATION > General Configuration > Content indexing
4. Choose Site reindex and Rebuild
5. Click Rebuild in popup

Expected Results

Reindex progress in progress bar should match progress in log

Actual Results

Reindex progress in progress bar does not match progress in log.

For example, when progress bar shows 31% , the log shows 77%.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available