Trial spawners only work once when spawned in creative

When you spawn a trial spawner in creative and put a mob in it, it will trigger once, and once cleared, will not work again until a spawn egg is used on it again. I am making a minecraft server where I am using trial spawners to work as the mob spawners and this is really making it difficult. Does anyone know any way to make the spawners work multiple times without having to be refilled?

Basically once triggered once, the mob in the spawner disappears, the loot is given, then it has to be refilled with an egg.

I have seen ONE post about this, and somebody just said that this wasn't true and the post was archived. I have done the testing myself and I KNOW this is true.

Questions likely to be asked:

Q: Is the spawner on cooldown? A: No
Q: Are you using mods? A: Yes, but I have tested and it is the same result regardless.
Q: What version? A: 1.21.1 Java