Airplay not working on my network

Hello,

I have a RT-N66U with a tomato version by shibby : 1.28.0000 MIPSR2-138 K26 USB AIO-64K

The Airplay on my network is not working the way it should.
Basically it works and after a few moment it stops... no idea why. After a reboot it is back...

I used to have a previous version of shibby and it worked... but not now. I do not know if it is the way i configured my routeur or not...

Anyone had this problem before?

Thanks for your help