One NIC suddenly stopped receiving most UDP broadcasts

Question

Windows 10, Killer E3000 2.5GbE adapter, the latest driver.

This started about a week ago without any changes that I can remember. I noticed it when Wake-On-Lan stopped working for this system. After trying to troubleshoot it, I found it's not limited to WOL, but also affects mDNS and just basic UDP broadcasts I send from other systems. The system still receives some UDP broadcasts, but much less than when using a second NIC (Killer E2600, 1GbE).

To test, I issue this command on another Linux system connected to the same switch:

echo "hello" | socat - UDP-DATAGRAM:10.0.3.255:9,broadcast

Adapter settings:

    E3000 settings:
       IPv4 Address. . . . . . . . . . . : 10.0.0.28
       Subnet Mask . . . . . . . . . . . : 255.255.252.0
       Default Gateway . . . . . . . . . : 10.0.0.1
    
    E2600 settings:
       IPv4 Address. . . . . . . . . . . : 10.0.0.29
       Subnet Mask . . . . . . . . . . . : 255.255.252.0
       Default Gateway . . . . . . . . . : 10.0.0.1

Only one adapter is enabled at a time, all the other adapters are disabled. Both adapters are connected to the same dumb switch.

With E2600 I can see the broadcast packet received on the interface. Verified using this tool and WireShark (in promiscuous and normal modes).

With E3000, the packet is never received on the interface.

The same can be reproduced with WOL packets sent from other systems and with mDNS not working at all (.local pings failing with E3000, but working with E2600).

What I tried and what didn't help:

• netcfg -d, netsh winsock reset, reconfiguring all adapters from scratch
• disabling all the network adapters except one
• uninstalling Hyper-V and its network adapters
• uninstalling OpenVPN and its virtual NICs
• disabling the firewall
• fiddling with adapter settings (offload, power saving, etc.)
• checking netsh dump for anything unusual
• rolling back the driver to several previous versions, including the old RTL8125AG one before it was renamed to Killer
• killer software uninstaller
• power cycling the switch
• updating motherboard (MEG X570) BIOS and verifying power saving settings don't affect the network
• explicitly changing interface metric of the adapter to 1

Everything else works just fine, I get the full 2.5GbE speeds, all the connections to all resources are working. When both E2600 and E3000 are enabled at the same time, the broadcasts are received correctly via E2600.

The next thing to try would be booting a clean system from another media and trying to reproduce the issue there. This will help to understand if it's some hardware problem with the NIC (firmware silently updated during a driver update?) or a configuration issue with Windows.

This issue really puzzles me. Any ideas?