Information in post#1 shows RTL8111/8168/8411 Ethernet Controller is using r8169 driver
Wired connection keeps dropping - #6 by nikgnomic
Manjaro hardware detection tool can install kernel modules for r8168 driver and blacklist r8169 driver
sudo mhwd -i pci network-r8168
Or use Manjaro Settings Manager GUI:
manjaro-settings-manager -m msm_mhwd
enable option in bottom left corner - Show All Devices
Look in section Network controller > RTL8111/8168/8411 for
network-r8168
Right click on
network-r8168
and select InstallManjaro Settings Manager should install r8168 driver for each kernel version on system and blacklist the r8169 driver