This release will be available starting December 19, 2018 and affects several themes.
IMPORTANT: This release is only available for SharePoint Modern versions and Office 365 Modern Themes.
Fixes
SharePoint Framework (SPFx)
We've fixed an issue causing a duplicate header to appear on certain pages.
Addressed a bug where settings were not propagating properly during partial page refreshes. Your configurations will now consistently apply even during dynamic content updates.