For multiple versions now there hass been a bug with the apothesis zombified piglin spawners.
First they spawn fine with no problems at all, then after some time "seems to be random" - they start to float in the air and take up spawning spaces until theres no space left to spawn. And when they float they arent real entities persé, i can kill them and they still stay there. I have to quit and join the world again for them to go away.