From my post on Reddit:

https://www.reddit.com/r/NintendoSwitch/comments/8u3dri/its_been_almost_a_week_with_the_new_minecraft/

My Switch Id is the same as the Xbox Id I use for Minecraft on my Win10 laptop. It just made it easier to tell someone my gt and know it was me. With that said, I made another Xbox Id for my Switch so that I wouldn't have any issues inviting myself to a cross platform game. Problem though. When hosting the game on my Switch, my character gets my Switch ID name. My Win10 copy then joins and is using the same name (original xbox id) so it gets a [2] behind the name. Not a problem initially, but when you try to put in any command with that player name you get a syntax error beacuse of the brackets. So '/tp player[2] player' won't work as you get the syntax error. You can't escape the brackets either. So the game gives the player a name you can't address or issue commands without causing a syntax error. Even the autocomplete puts in the bracketed number, but somehow the code to parse the command wasn't coded to handle the [].
Edit: Big thanks to /u/Alphatism for the solution here. Put the player with the brackets name in quotes. Ex: /tp "player[2]" player

I decided to make a report about this because when you are hosting a world and using the click dropdowns to auto generate a command, it should recognize that there is a name with brackets and automatically put in the quotes. As it stands you can auto generate the command: /tp player[2] player 
which will result in a syntax error.