Hi I'm back.
Still having the same problem, sometimes issue occurs wifi connected but no Internet.
Tablet has been for service twice and they can't find anything wrong, it works perfect in their network.
I have been experimenting with different settings in both the router and the tablet, and still haven't solve the issue.
The problem is that I don't know if the issue is in the tablet or router. Because other devices connected to the router is working perfect. Only when the tablet is connected at the same time as other devices and the issue occur the other devices also disconnect all at the same time.
But the tablet works perfect in other networks. This makes me crazy.
Also there is no consistency when the problem occurs, sometimes there's no issues for hours, and the next day it isn't working even a minute.
Also sometimes it reconnect automatically, sometimes the tablet can't find the network after switching wifi off/on after issue occurred and I have to reboot router, sometimes tablet can se network again but not connect because of authentication problem and I have to reboot router.
Any ideas what to do??!!