Problem solved. I had a very good support from Kathy.Z, TpLink tech support, . Issue understood, problem escalatated, fault discovered. The problem is in Tether app, next update will solve it. Many...

@David-TP Hi David, I did many power restarts but same problem. Yes, I received your mail Many thanks Lorenzo

In the "Network status" screen of Tether app the "Online duration" is not shown. Of course if I access my NX600 through browser locally (192.168.1.1) I can see the online duration time. I have two 5g...