For the custom biomes you can make, there is an option for particles - almost every particle works except for falling_dust, block, and item.

No error message is given when these particles are not working, unless I shove a bracket to where it doesn't belong, it will tell me everything is working.  I have tried multiple times and asked around the community for help, just to make sure I'm not doing it wrong and everyone agreed it wasn't any errors I was making.  They too also had no errors come up, even when it did not work.

I have tried in various ways to make this work and try to get error reports.  One of the strangest things I did was use a different particle such as end_rod and have the settings for the falling dust I wanted and the end rod particle effect worked with those extra settings!  Yet, still no error even with this working effect with extra settings that shouldn't be with it.

There are only 4 particle effects that have additional information that needs to be added for them to work, but only 1 of those actually works and that's the dust particle.  I had originally believed that it just couldn't work for more complex particles, but now after finding out that dust will work and the others won't, I'm dumbfounded.