Not entirely sure of what is causing this or the conditions for this to occur, but some commands when used in playerservers cause the player to get kicked. Some examples that I am aware of are /report, /f (not /friend though, strangely), /rules, /ban and /kick.
This is a big issue, as it means that different commands must be used in order to do what these commands would do, causing confusion for players.
It's a known issue that we haven't found a solution for. It happens because those commands are actually taken by bungeecord. We used to forward the command further to the server if it was coming from a playerserver but because of the new chat signing, 1.19 clients for some reason reject it. We haven't found a suitable solution for it though.
i’ve had the issue on earlier versions of the game too, when i’m on 1.16 i get the kicks