Do you have everything installed on your system, not on a networked drive? That includes the paths to the projects and the cache (under Preferences)? Some users even report issues when using OneDrive (I don't have them).
Try clearing the cache, eventually selectively by using the dcache AIR application. Be careful not to clear the cache of the project which could be converted to a backup. BTW did you try the backup version?
Clean the Preferences: find the subfolder 'utils' under the installation folder, and run the 'CleanPreferences...' appropriate for your OS while Captivate is closed.