A specific server lags and i can't move my cursor

On A server PixelBlockMC ip:best.pixelblockmc.com i typed /disguise Villager and i disuguised as a villager but if i wanted to type /undisg game crashed or if i play PixelBlockMC game lags i cant move cursor and i need to restart PC because i cant close minecraft this only happens on this server not on singleplayer or other servers (im flying but on this server you can get fly by reaching rank advanced+ or getting fly vouchers so im not getting kicked for cheating)