I have a few suggestions:
Check if there has been a bios update since April.
Do a hard power down and reset your bios.
Disconnect any other network devices that do not require troubleshooting. This includes LAN cables, USB to Ethernet adapters, and USB phone tethering. Turn your wifi off via your function key(s).
Power down the laptop and remove the battery and power plug. Let the laptop sit without power for a few minutes. Then, hold down the power button for approximately 30 seconds. Pressing the power button will help drain all left over power from the unit’s motherboard.
Then reattach the AC power (no battery), and restart. Boot into the BIOS settings utility and reset the BIOS back to the factory default and save the default settings. See if it will boot correctly with the factory default settings. If not, you may have to change a few settings in the BIOS (such as secure boot) to get Manjaro to boot correctly.
After restarting check your connection for any changes.
Also try this:
This is a script that should reinitiate your connection (hopefully this will help).
Create the script with an appropriate name and location such as:
Add the following contents to the script:
sudo -u $USER /bin/bash -lc 'nmcli networking off'
sudo systemctl stop NetworkManager
sudo ip link set eno1 down
sudo sleep 1
sudo modprobe -r r8168
sudo modprobe -r r8169
sudo modprobe r8169
sudo ip link set eno1 mode default
sudo ip link set eno1 up
sudo systemctl start NetworkManager
sudo -u $USER /bin/bash -lc 'nmcli networking on'
Save the file, and exit the text editor.
Be sure to make the script executable:
sudo chmod +x /usr/local/sbin/lan-restart.sh
Launch the script: