Hey so I just used ubports to flash on my pixel 3a and I was stuck at the same spot scratching my head for a bit. Once you get to waiting for device ADB is scanning and you have booted into the ubuntu recovery unplug your phone from the USB cable then plug it back in. That got it working and everything went well after that. I loved the OS but had to revert back to android I cant reliable get phone calls or SMS.

@dieharddan Not yet, sorry. Also my primary SIM card is in my Xperia X right now, will let you know when I had time testing MMS on the Pixel 3a.

@fredldotme got it thanks!

@monkeyman did it stop working after an update?

The UBports installer should be able to reflash it when you select the device manually and boot the device with Vol+ & Power pressed. In that case make sure to select the bootstrap option when installing.