Comment 2 for bug 2021409

If the primary issue is that other devices can only resolve your hostname after restarting avahi-daemon for a short time, plus, this machine doesn't see anything else on the network, it means that for one reason or another mDNS packets on port 5353 are not making it back to this host.

The overwhelming majority of such cases are due to a bug in the driver for that network interface, almost always its a wireless interface or some kind - it's rare in wired ethernet drivers but not impossible.

Very often setting the interface to promiscuous mode will fix this, because it tells the NIC to receive all packets (by default NICs filter out packets not intended for the host). You can try this command to set it:
ip link set ens160 promisc on

If this solves the issue, then it's 100% a buggy driver and I cannot do anything about that at the avahi level. You'll need to look at getting the driver fixed. This is common with bad wifi drivers, very rare with ethernet.

If that doesn't help, it could be the driver also doesn't support promiscuous but I've not really seen that before. I would then check
- Firewall on this machine,
- Any features of your wireless network such as "multicast dns optimisation", etc

If you run tcpdump for port 5353 you'll see packets coming and going. I suspect most likely your machine never receives any query packets from another host. So you can try run this command and then running a query from another host:
sudo tcpdump -ni ens160 --no-promiscuous-mode port 5353

You can also try this without "--no-promiscuous-mode" (by default tcpdump puts the interface in promiscious mode, same as the above command).

As a final note the resolvectl/resolved mdns support is totally independent of avahi, having it enabled could cause mDNS to fail in some cases - particularly with a network that performs 'multicast dns optimisation' where the packets are converted from multicast to unicast. Only a single process can bind to port 5353 for unicast packets and the packets will randomly get sent to resolved, avahi, chrome.. or any other process listening on port 5353. So disabling it (and anything else listening on 5353) could help in some specific circumstances though usually not necessary in most cases.