As per the title, was not able to log in to the site using either option - manual sign on was done using MyCrypto's message signing feature, and was verified as correct using Etherscan. The site threw a red box at the bottom with an error along the lines of "signature doesn't match". Subsequently tried to use MetaMask, connect a hardware wallet, and log in directly through the site option. This for whatever reason didn't work either.

Manual sign on is not an issue on user end since the message was verified by a 3rd party, MetaMask may be an issue on user end (although both FF and Chrome were tried). At the very least fixing manual sign on should be a high priority as everyone can use it quite easily.