Network Manager drops connection and hangs the system

Hello everybody,

I have got an annoying problem with the Network Manager (or wifi card?) which I do not know how to solve. No luck with search either. Can anybody help please?

have a Lenovo Yoga 910 with dual boot – Tumbleweed (20180525) with KDE / original Windows 10. The wireless card is Qualcomm Atheros QCA6174 802.11ac Wireless Network Adapter. Needless to say the wifi works under windows, so no problem at the other end or with hardware. But I need linux for work.

Here is the problem. The card is recognized, the connection is established (I use Network Manager), internet works for a while - that is, for about 10 min. Then the connection drops for no visible reason; the NM shows orange exclamation on top of its usual ‘fan’ in the system tray. Its status changes to: NetworkManager state is now CONNECTED_SITE as reported by journalctl -fu NetworkManager. No internet – pings do not work.

It may or may not go back to CONNECTED_GLOBAL (which is when the internet works) on its own, but only after a considerable delay like 15min. The connection may be reestablished manually by disconnecting/connecting in the NM. After a few cycles the NM goes off completely: its icon shows a red cross like in the airplane mode, available connections are no more visible. If at this stage the NM is restarted by

systemctl stop NetworkManager;  
systemctl start NetworkManager;

the system hangs completely, only hard reboot helps.

Any ideas how to fix it?