Ubuntu Server drops internet connection, resetting router restores (wired)

Question

My Ubuntu Server (18.04) will suddenly lose all internet connection, after running fine for a few minutes to a few hours, can't ping 8.8.8.8 or hostnames. Local network works fine.

It happens with both DHCP and static IP in /etc/netplan/50-cloud-init.yaml

Rebooting the server doesn't fix anything. Only rebooting the router restores internet.

Weirdly, DHCP works, and I will successfully get IP from my router, upon reboot or restarting network on the server.

running ifconfig -a gives following on my wired connection. (I have a ton of other interfaces, that I left out, from having docker running on the server)

enp0s25: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.99  netmask 255.255.0.0  broadcast 192.168.255.255
        inet6 fe80::3e97:eff:fe3b:f588  prefixlen 64  scopeid 0x20<link>
        ether 3c:97:0e:3b:f5:88  txqueuelen 1000  (Ethernet)
        RX packets 286557  bytes 39798935 (39.7 MB)
        RX errors 0  dropped 63  overruns 0  frame 0
        TX packets 407440  bytes 427684619 (427.6 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 20  memory 0xf2500000-f2520000

And ethtool enp0s25 gives:

Settings for enp0s25:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: on (auto)
Cannot get wake-on-lan settings: Operation not permitted
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes

I'm unfortunately not very strong in the internals of linux/ubuntu to know how to troubleshoot this issue better. There are no indications in the logs in my cockpit interface.

I've had the exact same networking setup running fine on a ubuntu desktop for months - same router, routersetup and switches/cables.

Can anyone point me in the right direction?