This is a bug I recently ran into, and tested it to be sure it was actually the cause.
My passwords use many unicode characters throughout them, including: !, @, #, $, %, &, *. But, when trying to log my account into ROBLOX for Xbox One it would not allow me to. Every time I tried to log in it would give me “Trouble communicating with ROBLOX servers. Please try again. Error Code: 901”. I can confirm that this is the cause, because when I remove those characters from my password it allows me to log in, with the same length password.
Hopefully this issue can be fixed in the near future.
Thanks!