UPDATE: Even with power saving switched off on Samsung mobile it occurs time to time. I just need to disconnect and reconnect. Anybody managed to find root cause and resolve the issue? Last 2 days...

@BobMuk Hi, did you manage to resolve the issue? I just bought M4 set today, similar setup (AP mode, Ethernet backhaul, 1gbps lan, 1gbps downlink/150mbps uplink, units randomly connected to switches...