The Health Dasboard provides you with an overview on the Sync Core status, potential configuration issues and a summary of failed imports or exports along with the reasons for it. Digging deeper, you also get an "Entity Status" page that gives you the status of every single entity ever exported or imported on the site along with actions forcing their import or export. The overview looks like this (see below for an explanation):
Sync Core
This is a list of all Sync Cores connected to the current site. You will see the version of the Sync Core along with some import and export stats for the current day. if there are any warning or error messages from the Sync Core, they will be listed here as well. If you enable the "update" module from Drupal Core, this site will also tell you whether you're running the latest stable version of the module and Sync Core or should upgrade.
Config Issues
When updating entity types by removing, adding or changing fields, you will need to re-configure your Flow configuration. To see if there are any Flows that require an update you can check the "Local version differences" on this page. The "Remote version differences" will display any remote site that uses an Entity Type definition that is different to this site, i.e. using different fields for the same entity type + bundle name as on this site.
Sync Issues
If an export or import fails, you will get a summary here. To get additional details, please check out the "Export" and "Import" secondary tabs on this page.