You know how it sometimes kicks you for sprinting at the beginning of a game. I got kicked for flying when I was trying to go solid. I was standing still.
Sometimes when the server takes a while to start the game and you are running away from spawn you will get kicked because the server thinks you are hacking. Getting kicked for turning solid seems new to me as that never happened to me before. Did you try to hide on another player? Because then you will obviously get kicked for flying as there is no block in normal minecraft sense. Hive has a custom version of the best anto cheat plugin out there. If they changed the settings in NoCheatPlus even a little bit we would probably see people using flyhacks and other hacks (I have seen that happen before). The Owners won't ruin the gameplay because someone gets kicked in maybe one out of hundred games. Also a way to fix the problem when spawning: Just wait until the scoreboard has loaded and you can start running all you want. As this is nothig that will be changed and I provided you with a simple way to not get kicked I will request a lock now.