Now part of the problem with LibreSignal was the trademark violation of using the name Signal. But Moxie is clearly against any third party using their servers, as we can see in this comment: https://github.com/LibreSignal/LibreSignal/issues/37#issueco...
IMO that's an unforgivable stance towards third party clients.
I have read (well, skimmed) through their terms of service and haven't seen anything against using their servers from third party software, yet they'll evidently shut down third party software for interacting with their servers. If you're gonna have policies like that, at least outline them in your ToS.