I have been trying to use the device sync for a while now. I forget when it was launched but I think I set it up right after it was launched. I was having issues with it and I could not figure it out. It seemed like one device would work with my external wallet but others would not.
Then today it dawned on me. I'm not even sure how I did this but I had saved by seed and then enabled sync on other devices but was never asked to enter my seed. So I think the issue was cause by me basically enabling sync on different devices and not using the same seed.
The solution was to disable sync on one device. Then log out. Log back in and enable it again. Copy the seed. Repeat this on all other devices. Now it works.
I don't think this is a bug. Maybe it is but it is a UX issue for low IQ users like me. Maybe it could be fixed with more clear instructions about logging out.
If anyone else is having issues maybe try to do what I did.