Why doesn't anybody fork the Signal clients? There are so many bad design decision in the clients (for instance no message backup on iOS or no way to save all media to storage automatically) that I don't understand why people accept the Signal Foundation's stewardship of the client code.
Molly[1], a fork of Signal, seems to work fine. I've used it for a long time and never had any issues with it (and it connects to Signal fine). But for security reasons one of their changes was dropping SMS, so switching to it won't do you any good there.