It could be the same thing that happened to me. The dev could have realized what people were using it for and quit to not be a part of that.

I used to run an encrypted messenger called Tunnelgram. It had some advantages and disadvantages compared to something like Signal (signing in on multiple devices, the web, you didn’t need an existing device to set up a new one, the chat history was saved on the server (encrypted), groups were easy to manage and new users could be added on the fly and see all the old messages, but it didn’t have forward secrecy (if someone got your key, they could see all the messages you sent in the future)). After Jan 6, and reading about how the insurrectionists planned their attacks on encrypted messengers, I just didn’t want to be a part of that anymore.