after finishing the editing process for a slide and try it for several times. suddenly it starts missing items of the design by stop executing pre-designed actions.

and therefor it keep this behavior and all project go in error

Hi Hany
You don't say if this is in production or after publishing
What you should try is to go back into courselab and if you can open the module; then from the drop down menu go to Module and Update objects.
This should refresh the code that is used to draw the components when the module is rendered.
If the module won't open at all it often returns a code, often it is something that sounds like an unexpected character has been found. Go to the location it gives Line x and character position y , you will often find a character there that is wrong.
This kind of thing does happen rarely and it is usually something corrupting the files. Unfortunately it can be difficult or impossible to recover the content.
I've had this happen in the past so I tend to keep a mirror copy of the most current working version of any work I am doing. I can then drop back to a slightly older version of the module if I need to.