Hi SimoR79, and everybody!
My experience ist the same: Some preview versions back, the problem seemed to be solved, at least for my Lumia 650. Then, when the new production version came out, it was back.
At the moment, I am on the production version, and I still have the problem. I already reported earlier that I evaluated the log of my router and simply put the exact dates and times when WiFi dropped into an Excel spreadsheet. Then I calculated the time between two events. It is easy to see that it is not just coincidence when the WiFi connection drops: The time between two "dropping events" is always (!) exact full hours or at least exact full 10 minutes. Try yourself. Example: First dropping event at 9:41:13 am. Next dropping event the next day at 7:31:13 am. Time between the events: Exactly 21 hours and 50:00 minutes. And it is always like that!
The first conclusion is that there is a plan behind this behavior of the WiFi connection.
The second conclusion is that it should not be that difficult to solve the problem: Just remove the "counter", and everything is fine! Just kidding - or not?
Have a sunny weekend!