Just passing this along in case it helps someone. I was setting up a new EdgeRouter X using the basic option. Firmware updated to v1.9.0. I changed the default password, and when I saved the config, it would NOT write the change. I would see a vague error flash by but I could not figure out why. On a hunch I removed the "@" I had in my password and it saved the config. Bingo, it worked!
I have not seen any documentation on forbidden characters in a password. If anyone has that info please pass it along.
Thanks!