A user, who checked out a project in WebStudio works on a copy of the project stored in RMS project source directory. The project source directory has been configured in RMS.cdd file, using property "ws.scs.rootURL".
When you modify the project in RMS project source directory the local copy of checked out projects in WebStudio is not updated automatically.
The user has to perform the Operation "Sync To Repository" to load the changes to the project in his workspace.
 

Which Artifact changes are synchronized by WebStudio Operation "Sync To Repository" when project in RMS project source folder was modified.

All Operating Systems

The WebStudio operation "Sync To Repository" returns modified artifacts only (e.g. added new property to a Concept/Event).
It will not sync/return newly added entities.

The "Sync To Repository" feature was designed to handle changes around existing non-managed artifacts by WebStudio. 
That means all changes around adding new properties to existing concept/events or changes to VRF or Rule Templates.

If you add new artifacts a better approach is to create a new project version.
When this is not possible delete the project from user’s workspace and uncheck it again.

Note:
ER BE-29137 created to return new added entities

Artifacts managed by WebStudio (DecisionTables (DTs), RuleTemplates (RTIs)) not reloaded from RMS source directory. 
The WebStudio Operation "Sychronize ..." used to check and return artifacts (DTs, RTIs) modified and committed by other Users.