"(So closing the updater is maybe a key step!)"
CLOSING THE UPDATER IS A KEY STEP..... I just did the same thing @grdGo33 did with reuploading like 5 times to no avail. I originally had 1.11, went to 1.21 and the update failed so I downloaded Line 6 Updater and each time I tried to download 1.11 again it would fail, but closing the Line 6 Updater software, turning off my pod go, turning it on and then immediately sending it to the updater setting (hold down the right page button) and then spinning up the Line 6 Updater did the trick!
Not cool Line 6, very very tricky. I'll try updating over to 1.21 now that I know this trick and can unbrick the pod go now after an hour and a half of troubleshooting.