Import / Sync Favourites / Hidden not working

Fire TV App: 3.0.3
Server: 2020.12.05.2308

Might be a Telly-ism, as I use this currently between my m3u source and Channels.....but then it might not...

I made some changes to my channels on the media server - numbers, added a few more, changed some hidden/favourites. Then I noticed that channels that I had hidden, were still showing in the Fire TV App.

So, I tried the 'Import from Source' but all it seemed to do was wipe out ALL favourites and any hidden locally on the device. Clearing cache/data on the App, then relaunching, it re-read the correct favourites/hidden channels from the server.

I submitted diagnostics about 10-15 minutes ago, on the final Fire TV that I needed to fix - seemed to be an issue with all 4 of them.

P.S. Is there a way to make sure that all devices are always synced with the server for favourites/hidden? I'd want all channels to always be in sync with the server, ideally, and not have to manually sync changes?

Probably related to Telly. I don't think the new M3U sources would have this issue.