Wake on lan stopps working

Hi

I have setup Teamviewer for wake on Lan from outside.

DynDNS in my router is activated and a static DCHP adress for the wished PC is added. 

The port 13579 is forwarded to my PC too. 

This works really easy and nice. From Lan  and from outside.

After a while of not waking or using the PC it stops working.

Thanks for your help!