enp3s0 (formerly eth0) does not connect anymore

my computer can only connect to my network via wifi for a week now. In NetworkManager’s journalctl output, I find:

journalctl output

Nov 04 17:35:06 aeon NetworkManager[549788]: <warn>  [1604507706.0747] dhcp4 (enp3s0): request timed out
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0748] dhcp4 (enp3s0): state changed unknown -> timeout
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0748] device (enp3s0): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0752] manager: NetworkManager state is now CONNECTED_LOCAL
Nov 04 17:35:06 aeon NetworkManager[549788]: <warn>  [1604507706.0762] device (enp3s0): Activation: failed for connection 'Wired Ethernet'
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0766] device (enp3s0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed')
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0798] dhcp4 (enp3s0): canceled DHCP transaction
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0799] dhcp4 (enp3s0): state changed timeout -> done
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0808] policy: auto-activating connection 'Wired Ethernet' (a6466101-ff2c-4d4c-b898-de5be7932c85)
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0813] device (enp3s0): Activation: starting connection 'Wired Ethernet' (a6466101-ff2c-4d4c-b898-de5be7932c85)
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0814] device (enp3s0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0816] manager: NetworkManager state is now CONNECTING
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0818] device (enp3s0): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0824] device (enp3s0): state change: config -> ip-config (reason 'none', sys-iface-state: 'managed')
Nov 04 17:35:06 aeon NetworkManager[549788]: <info>  [1604507706.0827] dhcp4 (enp3s0): activation: beginning transaction (timeout in 45 seconds)

NM output (notification bubbles)

"IP configuration was unavailable"

Manual dhclient call

root@aeon:~# dhclient -v enp3s0
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp3s0/d4:5d:64:52:c9:c1
Sending on   LPF/enp3s0/d4:5d:64:52:c9:c1
Sending on   Socket/fallback
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 2 (xid=0xf30ecf3e)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 2 (xid=0xf30ecf3e)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 2 (xid=0xf30ecf3e)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 2 (xid=0xf30ecf3e)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 2 (xid=0xf30ecf3e)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 1 (xid=0xf30ecf3e)
No DHCPOFFERS received.
No working leases in persistent database - sleeping.
^C

What works

wifi works, dhcp returns in an instant.

Things I tried

1. changing the dhcp provider in my NetworkManager.conf to internal or dhclient.
2. Deleting old leases in /var/lib/NetworkManager/.
3. I made sure I have the empty file /etc/NetworkManager/conf.d/10-globally-managed-devices.conf in place.
4. Tried to create a static network ip connection. Well, it connects, but I do not get any data through.

Current NetworkManager.conf

[main]
plugins=ifupdown,keyfile
dns=dnsmasq
#dhcp=dhclient
#dhcp=internal

[ifupdown]
managed=false

[device]
wifi.scan-rand-mac-address=no

lsb

root@aeon:~# lsb_release -d
Description:    Ubuntu 20.04.1 LTS

netplan files

root@aeon:~# ll /etc/netplan/
total 24
drwxr-xr-x   2 root root  4096 Apr 23  2018 ./
drwxrwxr-x 208 root root 20480 Nov  4 20:10 ../

Ok, I do not know what to do next. I think I had a netplan.io apt-update from 0.99.x to 0.100.x, but downgrading didn’t help either. Any suggestions are much appreciated!

What you should do whenever you are not receiving IP address with a wire cable :

1. Test your network has no short, try another cable.
2. Check visually if pins inside network port are not broken (both side, computer and switch/router)
3. Check network light activity.
4. Try to plug on another network.
5. Try to do a power recycle : power off your computer, unplug the power supply, long press the power button during 30 seconds (of course computer will not powering). Plug back, switch on and test again.