We have had a Vivofit Jr. 2 (BB-8) for our eldest child for 4 months without any major issues. We just bought a new one (Minnie Mouse) for our youngest in the Garmin 30% sale. It arrived with firmware 2.10 and I was able to set up and sync it to my iPhone 11 Pro (iOS 13).
However every attempt to have the firmware updated to the latest 3.00 version failed. The watch showed the update symbol for a few seconds and then a tick, and then rebooted. The iPhone stated firmware update failed. Also tried on my partner's iPhone with the same result.
I was going to request a replacement from Garmin but decided one last time to try, so this time I selected to add a new garmin device in the iPhone app under our youngest child's profile (even thought it was already added), and just left the watch and phone together while I ate dinner. When I returned the watch had updated to 3.00.
So I'm not sure what the underlying issue was, and what specifically ended up making it work in the end, but now it seems to be ok.
Am sharing in case others have similar issues and are looking to see if there are any solutions.
TheSalamander