Particle emitters in Godot have forests upon forests of settings, and I’m guessing that’s why Bram supplied ready-made particle scenes for now instead of diving head-first into them. There are probably plenty of potential causes for what you’re seeing.
I’m going to assume that you have either modified Bram’s provided particle systems, or you have made your own from scratch, because Bram’s emitters worked fine when I tried them.
I would suggest downloading the provided particle scenes (fresh copies if you already did so), and then looking through the settings of both yours and the provided ones to identify any differences. Because .tscn files are plaintext-based, if you’re on Windows, you could also try using WinMerge to look for those differences automatically (and if you’re not on Windows, I’m sure there are other programs that do the same thing). It’s a fantastic little tool.
https://winmerge.org/
Good hunting =)