Certain character combinations are automatically converted to emojis to save you having to go to the emoji button and add them in. I find it quite useful, but because the close bracket ')' character is used for a lot of the smiling emojis, it cuts down your options, especially with lists. You'd have a similar problem when you got to D.
Going forward, you could either use lowercase letters, i.e. a), b), c) etc., or you could put a space in between, i.e. A ), B ), C ).