Go into your Routers web-page. Direct connect a LAN between PC and Router. Look at the settings.

If you can activate both 2.4 and 5.0GHz simultaneously do so.

I am not 100% certain this is your problem though but it should give most current Beo-Net products to switch up to the 5GHz automatically and take the load off the 2.4GHz band.

Have you checked if there is any critical events listed in the Diagnostic section of the A9 setup page?

NVGAE wrote:

(and the A9 is just next to the router and always shows excellent network strength)

A bandwidth issue would not make the device unreachable.

In NVGAE's case it seems that the device is able to connect to the Wifi network, join the BV in a multiroom setup but is no longer reachable through the app after some time.

@NGVAE: What I don't get is that the A9 is playing music in a multiroom setup through the BV while you try to change the music by trying to connect to it via the app, this means that the A9 is on the network, doing its job but you don't see it through the app. Do you see the BV through the app? Is the A9 setup to play music independently of the BV, i.e. has Dezzer, Tunin or DLNA configured?

Fyi: My A6 has issue reconnecting to the WiFi if the latest has been turned off then on, only an A6 power unplug/plug solves the issue. B&O ack the issue, but no fix so far. I wired it.

I don't get this either, the same applied on my old BSM. What happens is that I open the app and I push the beoplay A9 and it shows as nothing is playing. Then I try to go into the A9 (set-up page) and then the app just thinks and thinks and thinks. I tried powering off the A9 and turning off my phone and on again (iPhone 6) and the same happens. The only way for me to resolve this (so far I know) is to hard-reset the A9.

The funny thing is that this only seems to happen when I'm playing in multiroom. If I only play music on my BSM or A9 everything works smooth. When I connect a product via multiroom this happens. 

And yes it's very strange that music continues to play. Even stranger was that when this happened between the A9 and BSM, I could manually joing the A9 to a BSM multiroom stream by tapping on it, but I could not reach it in the app. 

And yes the A9 is set-up to play music independently, has deezer and tunein.

I had similar problems with the BSM, but then the BSM would just give up and go mad (happened when the tech guys were installing the TV and they took it with them and are now sending me a new one).

I just don't understand where the problem lies. Is it my router-config or is it the B&O products and then what product :S 

Because the A9 works fine on its own, the BSM works fine on its own, the Horizon works fine on its own but when in multiroom all runs havoc on multiple levels. 

Can you try the following URL against your A9 when no longer reachable via the APP:

http://xxx.xxx.xxx.xxx/index.fcgi# where xxx.xxx.xxx.xxx is your A9 IP address.

If reachable this way I would question the APP, is it running on IOS or Android?