If you used "/fill" or "/clone" to break the spawner, then this is "MC-46094 - Using fill/clone which replaces mobspawner and keeps its fire particle".
We were playing in survival when this happened, however removed it by breaking it in creative. Did not use any commands.
Thank you very much, solved the issue
Multiple pistons getting powered by a redstone clock to push the blazes into a funnel for a farm.