balenaEtcher unable to burn tails to newly erased/formatted USB drive

trying to burn tails to a USB, formatted to Mac OS extended (journaled) with GUID Partition Map.

On every occasion whilst flashing Tails to the erased USB it suddenly appears to disconnect from finder and won’t reappear after the flashing is complete (shown in the screenshot). I have tried this several times and have also restarted my computer to try again. Have tried on two different USB drives (both over 8GB) and have had no luck.

not quite sure if the resulting USB would be visible in MAC OS. Have you tried if the USB actually works as intended ?
Otherwise in etcher you can press Cmd+Alt+I as explained here and supply the logs you find in the console tab for further investigation.