On the first time (with an out-of-the-box) Ubuntu Core device I try to do snap refresh and get the following result:
Error: cannot refresh: cannot refresh snap-declaration for “tpm2”: Get
dial tcp: lookup api.snapcraft.io on [::1]:53: read udp [::1]:45649->[::1]:53: read:
However if I leave the device powered up and connected to the internet over night it the automatic overnight update works and in the morning when I try snap refresh, I get the result "All snaps up to-date). Nothing else had changed on the device/network environment in the meantime.