when i spawn farm animals on my 1.9 server they immediately disappear

i was on my 1.9 mini games server and i tried to summon a chicken for a game but nothing happened so i tried again and this time i saw it flash into existence before disappearing. i tried to reproduce this glitch on a single player world and it was fine, then i tried again on my server with cows and creepers the creepers were fine but the cows disappeared!?!?!?! HELP!!!!!!