Unhappy [solved] [Q] P900: Wifi PSK issue

//EDIT: it seems my P900 is the victim of a 'strange' network configuration and nor the specific hotspot is the source of the problem.

I am sitting at work and we have a 2,4 Ghz Wifi with Enterprise PSK.

My brand new P900 connects to it but after a minute or two the network traffic dies silently.

The app wifi analyze tells me the connection is very good the whole time. So there seems to be no problem.

What I have done so far:

- deleted wifi connection from device and made a cache wipe
- completly wiped the whole device.

Nothing helped. After a short reconnect the net is back but it dies the same way as described.
Same network thethered over my Samsung S3 via Bluetooth works but that is not a good solution for me.

Any tip how to solve this issue?

I would try any method including root but afaik there is no way back to unroot and return device to vendor because of this knox flag?