[popcornmix]

If I connect directly to the tv it works everytime and connected first to the receiver and then TV it dont work but I found a workaround.
I connect the Pi to the tv and start a movie with "Full 3D Enabled", it works and the Pi is sending FP.
I now connect the Pi to the receiver without turning either tv or Pi off and it works now too and that is confusing.

Its like the Pi needs to know that the TV and receiver can display FP and for me it looks like a handshake problem.
If it dont work the receiver isnt displaying that it has a audio signal, it shows only "decoder off".
2D works every time with the same 3D file.

With "Use Full HD HDMI modes for 3D" disabled does it work every time, or still fail?

Can you first add hdmi_force_hotplug=1 to config.txt (and reboot). Not expecting it to fix anything, but removes a variable in the following tests.

A couple more experiments may be interesting. If you play the 3D video and get a blank screen. Can you:
Power the TV off and on again.
Change AV input away and back with remote on TV
Power the receiver off an on again.
Change AV input away and back with remote on receiver.
Unplug and then replug hdmi cable from receiver to TV.
Unplug and then replug hdmi cable from Pi to receiver.
Unplug hdmi cable from Pi to receiver and directly connect it from Pi to TV.

Do any of those make the picture reappear?

Can you also add "config_hdmi_boost=7" to config.txt (and reboot). If that doesn't help try "config_hdmi_boost=11".
I don't think that will help, but it's a simple thing to rule out. If it doesn't help you can remove it.