I can't sync the rushes I have added

Synchronization is sending your project from the application to the platform. However, you must be vigilant during this step. Indeed, some bad handling can cause a bad synchronization which will cause the disappearance of some/all your rushes but also it would be impossible for you to read them.

To avoid this kind of concern, we recommend:

Submit your project using only the application or platform.
Avoid going on the project on the platform during synchronization.
Avoid putting your instructions during synchronization.
Avoid any action on the project during synchronization.