@oyierphil - This looks to be a public instance - would you mind sharing the URL? We can then debug the server to see if the it is configured correctly from a TLS perspective.
Without knowing, more, I would guess that maybe you didn’t load all the correct certificates such that the TLS chain doesn’t validate? This can cause desktop browsers to work but Android clients to fail (often cht-conf as well). You can check this thread for more information.