Created attachment 840655 [details]
lscpi of the realtek ethernet controller

a watchdog stops the network function (a bridge with one ethernet interface is
configured) on a Gigabyte Z68XP-UD3 motherboard with a Realtek RTL8111E network
chip (driver r8169). This is reproducible after a little network usage after
boot (e.g. working on a ssh session or doing some ansible commands over ssh)
and until the watchdog is stopping the network, the ssh session is reacting
very slow on the input. Then the bridge, the interface and the routes are still
present and up, but the network is not working.
There are no significant signs in the system log and on the higher network
level before the problem is occuring. 
I have 2 such identical systems, which are showing the problem and were running
stable on Leap 15.1. I have only tried the kernel 5.3.18-lp152.33-default.
The Leap 15.2 was installed from a image, which is running stable on other
systems (with other network cards and motherboards).