Yup, another one of mine! 

In my world, I have a command-block version of the Lucky Blocks mod. It uses the 1.12 /scoreboard teams command (long story how I got to that). I've been updating the world to 1.13, as I said in my solved Repeating Command Blocks a-mistake-that-was-mistaked-to-be-a-bug (my bad! ), and when I tried to update the commands, I noticed they do not work. I tried the command in chat:

/team join LuckyBlock @e[name=LuckyBlockSelector,limit=1]

When I ran the command

/execute as @e[team=LuckyBlock] run execute at @s run tp ~ ~10 ~

, that is supposed to teleport the target 10 block up (or 10 block above me, I don't know if that's the right command), it said "No entity found". There is no command block running the command "/team leave @e" or anything like that.

So, I believe this is a bug. Please fix it as soon as possible- I don't want my world to be corrupted! 

Thanks in advance, David Kleiner (MasterOfTheCats)