Not sure if this is caused by a mod or is just a bug that also occurs in vanilla (or if it's even a bug at all). Many modded particles are missing, as well as the fire and small smoke effects from candles/furnaces, the purple particles from endermen and the nether portal, as well as many environmental particles. I'm using ultra settings with Embeddium and Oculus as the main performance and shader mods I'm using.

Missing Flames:

Portal:

I found a few more examples:

Enchanting Table (letters floating from books missing)

Alchemist Cauldron (from Iron's Spells 'n Spellbooks) not producing bubbles

As a follow-up, so far none of the particles from Iron's Spells are appearing whatsoever.

Figured out what causes the particle to disappear (at least on my side). This is somehow tied to volumetric clouds, if that option is turned off particles return to normal. Attached images with and without volumetric clouds

Very strange. I'll have to check if that works for me.

Wow, that volumetric clouds thing really worked. That's so weird. Thanks for the fix!