I attempted to make this recipe
<recipeType:create:mixing>.addRecipe("icing_mixing", "heated", <fluid:contenttweaker:icing> * 20, [<tag:items:forge:crops/vanillabean> * 2], [<fluid:contenttweaker:molten_sugar> * 20, <fluid:minecraft:milk> * 20], 20);
Using a cusotm fluid and milk and vanilla beans to make a custom fluid called icing. this does not work no mixing occurs despite a recipe appearing in JEI
I changed the recipe to only use the molten sugar custom fluid, then proceeded with the following tests.
I added the recipe
<recipeType:create:mixing>.addRecipe("test_one", "none", <item:minecraft:diamond>, [<item:minecraft:air>], [<fluid:minecraft:lava>, <fluid:minecraft:water>]);
to test if it was an issue with two fluid recipes, which it wasn't as this made 1mb lava and 1mb water into 1 diamond.
next I attempted
<recipeType:create:mixing>.addRecipe("test_one", "none", <item:minecraft:diamond>, [<item:minecraft:dirt>], [<fluid:minecraft:lava>, <fluid:minecraft:water>]);
and this too worked, and made lava, water, and dirt into a diamond.

so then I re-added the second fluid to the original recipe and it instantly broke itself resulting in no mixing occurring.

Please upload your crafttweaker.log file to pastebin. (/ct log)

https://pastebin.com/4HDkgAPP

like this?

So I'm unable to reproduce,

I used the following script as I don't have those items / fluids in my game:

<recipeType:create:mixing>.addRecipe("icing_mixing", "heated", <fluid:minecraft:lava>, [<item:minecraft:white_wool> * 2], [<fluid:create:honey> * 20, <fluid:minecraft:water> * 20], 20);

Something to keep in mind, you set the recipe to "heated" meaning that it needs to have a blaze burner beneath it and that blaze burner needs to have fuel (that confused me for a while).

i have the heating set up properly, and in this case maybe ist an issue with content tweaker fluids?

It shouldn't be an issue with the contenttweaker fluid, is your script (the one adding the recipe).

Did you try my script to see if that one works?

i did not try your specific script no, but when i used my script using water and lava it worked normally

Yes but if you look, my script outputs a fluid, like your original one does, your other scripts don't. That is why I am saying try my script sin e it could be treating things differently

oh good point, i'll try that when i get home

yours worked properly as well

And replacing the water in my script with a contenttweaker fluid? Does that work?

that breaks it again

Then report it to Content Tweaker, since something with those fluids must be messed

done