X2GO Flashing client window while seeing Plasma host

[linuxfluesterer]

Hallo friends.
On my Sabayon, I have installed X2GOclient and on my Plasma 5.13.4 Gentoo, I have emerged X2GOserver 4.0.1.22  (host).
In my home I have a Gigabit LAN (network) with 100 MBytes/s transfer peak.
I achieved running x2go on both computers and I can connect with my client onto my host with settings:
- entered the correct ip
- 1920x1080 Pixels
- using the given Desktop gui on my client (Gentoo), which is Plasma 5.13.4

When I now connect with my host, enter the password to my username, I see the desktop of my already running Plasma 5.13.4 gui on my Gentoo.
But, in this x2go window the remote screen is flickering very, very much. Means background parts are changing with foreground parts.

The Gentoo (host) system has a video rate of 60 hz at 1980x1080 pixels, my client is a monitor with 3440x1440 pixels also at 60 hz.
The x2go host (Gentoo) is running in a 1920x1080 pixels window.
I can not change the rate on my Gentoo to a lower hz setting, which was suggested in a Google comment. Mode does not exist.

So, does anyone here work with Gentoo, Plasma 5 and x2go?
And more, did someone here experience the same behavior also? Is there a possible solution?

Thank you in advance.

-Linuxfluesterer