Kernel 6.14.3 breaks avahi mDNS and makes grabbing an IPv6 address unreliable (possibly MT7925 wifi related)

Description:

After upgrading to 6.14.3, I noticed that I could no longer ping *.local addresses provided by Avahi. I have Avahi and nss-mdns configured as described in the wiki along with systemd-resolved with MulticastDNS=no

I have also noticed on occasion that 6.14.3 will refuse to get a DHCP IPv6 address from the router, no matter how many times I reboot the router or reconnect with NetworkManager.

Reverting to 6.14.2 fixes both mDNS and IPv6 addresses immediately. Going back to 6.14.3 after recently booting 6.14.2 immediately breaks mDNS again, but the IPv6 address remains until sometime later when it disappears again.

This doesn't appear to be happening on my other devices. Only the PC with this MT7925 wifi card seems to be showing the issue so I wonder if it has anything to do with the round of fixes for the performance regression that landed in 6.14.3.

I tried to do a kernel bisection by following Bisecting bugs with Git and attempting to do it on linux-git as the kernel wiki page suggests, but I don't know how to tag the .2 and .3 point releases. I am assuming this is because it is using Torvald's tree. Not sure how to proceed here so if someone can point me in the right direction that'd be greatly appreciated

Additional info:

Steps to reproduce:

  1. Setup Avahi mDNS, and maybe systemd-resolved with MulticastDNS=no (not sure if relevant)
  2. Test that you can ping a *.local address of another machine in your network that's also advertising itself via mDNS
  3. Upgrade to kernel 6.14.3
  4. Ping again. Notice that ping does not go through.
Edited by Benjamin Xiao