It says if you disclose an invention after you left it is presumed to be made before you left. So if you leave, make something, then disclose it, they will presume you made it, left, then disclosed it.
The thing that is "presumed to have been made during my period of employment" is "any _such_ invention, discovery or item of intellectual property", and the "such" here refers to "each and every invention, discovery, (...) made (...) during my period of employment".
It's pretty redundant and there could be a fight regarding when the invention was made vs disclosed, but the wording limits it to the period of employment.
So what this says is that they have IP on inventions you made while employed, even if you only disclose that invention after having left.
It does not say anything about inventions made after you left.