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Internet/Wifi on laptop drops connection periodically

I have recently installed Ubuntu 18.04.4 LTS on my laptop, Lenovo Y50-70.
I noticed, that my internet connection (regarding whether it is wifi or cable) drops from time to time and then reconnects. No other device has that problem.

I find this disturbing, while working and I just lost hope.
I’ve tried things mentioned below (in this order, but nothing seems to be working, or I did sth wrong).
Below solutions are also gathered from the stackoverflow / internet.

1) Disable wifi power management

In /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
wifi.powersave=3 => wifi.powersave=2

2) Turn off IPv6

  -  /etc/dhcp/dhclient.conf
        Comment line nr 18: dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,

  -  disable IPv6 from GUI

3) Static IPv4 adress + DNS
4) Local-link IPv4
5) Ensure router works on 2.5Ghz
6) Change NetworkManager to WICD

    sudo apt install wicd-gtk
    sudo apt remove network-manager-gnome network-manager

I really can’t identify the issue. Nevertheless, I will be greatful for any other solution.

If you need any additional information, please let me know.