Monster spawners stopped working after updating of 0.12.1

After yesterday's official updating from google store to version 0.12.1, all the monster spawners of my survival map stopped working.
They appear with fire particles but with no monster inside. They spawn nothing, independently the difficulty option of the game.
That happens to both old spawners (found, while having the older mcpe versions), as well as on new spawners (found after updating).

Device: Samsung galaxy note pro 12.2 LTE - SM P905.