I've used getMACFromIP in an app for six months without issue, in order to take the hostname of another physical device on my local network (e.g., "upstairsheat" or "downstairsheat") and get the MAC address (which I need so that I can set a custom hubitat device's DNI to said MAC address in order to allow said device to post messages via HTTP to my hubitat device.)
This morning I suddenly started seeing this fail. Upon debugging I see that getMACFromIP is consistently returning null for every hostname I throw at it (all local devices on my network). If I manually look up that host's IP address (192.168.etc.etc) it works properly and gives me back the MAC address as it always has. Also, when I go to my Hubitat's network troubleshooting page, I am able to successfully ping these devices via both IP address and hostname -- so the Hubitat is able to resolve them. Also, "arp -a" on my windows box on the same network shows the MAC addresses of other devices, as I'd expect.
This might have started when I updated from 18.104.22.168 to 22.214.171.124 a few days ago, although I confess I am a bit surprised I didn't hit the error earlier. So maybe there is some very strange issue in my own router or network? Either way this is odd, but is anybody else seeing getMACFromIP working ok?