Yeah it's really unfortunate. I think having no communication makes it worse. If the developer would just say something, it would be a lot better. I hope they are doing well at least though. Sync has been such a wonderful app for so many years and I've used it since the reddit days as well.
Summit is also great too. Sometimes I will use it instead of Voyager/Boost. In the end there are a lot of decent and usable apps at least. It's a shame Sync is no longer viable.