I am having difficulty in ssh-ing into Raspberry Pis via their mDNS (avhai / zeroconf) .local host names.
After reboot I can ssh into a pi as expected:
$ ssh firstname.lastname@example.org
However after a period of time (it seems to be a day or two - but I've not measured it accurately) I can no-longer access the Pi's via their ".local" URI (ssh, ping, HTTP access, etc. all fail to connect); but I can still access the pi's via their IP addresses (e.g.
$ ssh email@example.com). A reboot of the Pi restores the previous mDNS .local host name.
This effects multiple Pi's (both Pi 3 & 4); and it happens with both WiFi and ethernet connections.
I'm running Raspbian / Raspberry Pi OS on the Pi's; and networking via OpenWRT on Linksys hardware.