monster spawners not spawning monsters

my spawners suddenly stopped spawning,

after playing in the nether for a while i was kicked out of server and promted for game update. after installing said update and returning  back to the spawner, i realized i was waiting super long for the mobs to spawn, after finding that the spawner remains intact and both zombie and spider spawners still had the single spinning mob in the middle of cage. waited over 15mins for one to spawn and nothing..... has anyone found a fix or is this because of the new update ?   please help,