I just had a friend of mine a state over install MC on her GalliumOS machine. Installation and registration worked like a charm but she can't seem to connect to my server through the cloud via port 52199 or 52200. For the former, I gave her my public-facing IP (XXX.XXX.XXX.XXX:52199), whereas I gave her what I'm assuming is my address as it appears to my ISP (c-XXX-XXX-XXX-XXX.hsd1.co.comcast.net:52200), this being the only way I've ever gotten the SSL connection to work. For the latter, I had her check the Use secure HTTPS connection, if available option in the File > Library > Connect to Remote Library... dialog. The non-secure address throws an Invalid address error, where-as the secure address throws an Error Loading Library. She says that it throws this error before any attempt is made by MC to download the library or any prompt for credentials appears.
I have traffic through ports 52199 to 52201 forwarded to my server's local IP and DHCP address reservation set up to ensure that said server always has that same IP (and indeed, it does). I checked my public-facing IP and it hasn't changed.
Using the secure address, she can access my Panel via her web browser using my read-only credentials. It complains about the untrusted certificate as expected but otherwise functions.
If it means anything, my server is running Windows 10 Pro. I just tried connecting my laptop—also Windows 10 Pro—to my phone's mobile tether and went through the same process above with the secure address but I can't reproduce the problem. Laptop connects as expected. So does the phone itself—Android 8.0.0—using MO 4Media and the same method.
I'm guessing she has some kind of out-bound firewall rule that's screwing around with this but I can't say; I don't have her machine in front of me and I don't know enough about Linux or GalliumOS to know off-hand how it handles connections and with what software. I'm hoping that this is a lot simpler than all of that.
Any ideas?