The ambient area Spore Blossom particles disappear overtime gradually caused by an unknown factor. The amount in the air will slowly go down until there is very few, and cannot be fixed by replacing the Spore Blossom. Only reloading the world fixes it in my experience. Note that my particles were fully enabled in video settings the entire time.

I can't tell if it simply happens over time or caused by an event such as player respawning/death/reloading chunks, but it's very apparent as the video shows:

SporeBlossomIssue_COMPRESSED.mp4