Carrier comes up and immediately drops endlessly

First time installer of OpenWRT; please be gentle. I didn't find anything relevant on a search.

I have a D-Link DIR-645 A1 on which I just installed verified firmware openwrt-22.03.2-ramips-rt3883-dlink_dir-645-squashfs-factory.bin. My laptop's Ethernet is plugged into port 1 (not the WAN port) of the device, and was useable with the factory firmware installed.

However, since installing the OpenWRT firmware, all I'm getting in my syslog from the Ethernet interface is this:

kernel: e1000e 0000:00:19.0 enp0s25: NIC Link is Up 1000 Mbps Full Duplex, Flow Control: Rx/Tx
systemd-networkd[1297]: enp0s25: Gained carrier
NetworkManager[1296]: <info>  [1667846273.5166] device (enp0s25): carrier: link connected
NetworkManager[1296]: <info>  [1667846273.5176] device (enp0s25): state change: unavailable -> disconnected (reason 'carrier-changed', sys-iface-state: 'external')
kernel: e1000e 0000:00:19.0 enp0s25: NIC Link is Down
systemd-networkd[1297]: enp0s25: Lost carrier
NetworkManager[1296]: <info>  [1667846274.5194] device (enp0s25): state change: disconnected -> unavailable (reason 'carrier-changed', sys-iface-state: 'external')

This cycles endlessly.

(This is after I assigned enp0s25 the static address 192.168.1.19/24. Prior to that, there wew additional messages about dhcp4 and mDNS trying to get going.)

Is this a known issue I just haven't managed to find described? Or a common problem due to my screwing something up?

Thanks!