Minecraft 1.12.2, Forge 14.23.5.2860
Universal Tweaks 1.12.2-1.8.0
(ConfigAnytime 1.0, MixinBooter 8.6)
Fairy Lights 2.2.0 for 1.12.2
(fresh instance; default configs)

Fairy lights mod has a crafting system similar to fireworks: you can craft a strand of lights and the recipe is customizable, you add items according to what lights you want on your strand.

But with Universal Tweaks installed, the crafts break or get stuck. There's two issues and I demonstrated them in this Youtube video but I will also try to explain below: https://youtu.be/XfwVI4-UoTg

First issue: recipe output stays even when item is removed.

1. Start with the standard foundation of iron ingot + string + iron ingot (nothing shows in output yet; you need to add at least one light item).
2. Add a "red light bulb" item to the recipe. Now the output shows a red strand of lights.
3. Add also a "green light bulb" -- output shows a strand of red + green lights.
4. Take away the green light bulb item. Still the output shows red+green lights.
5. You can even take the output, and it consumes only the red item that was in the crafting grid, but not the green item that you took out. The result is a real, placeable item, not a mirage.

Second issue: recipe can't be crafted the same way twice.

1. If you do the above, then go back to the crafting grid and set it up exactly as you did the first time: iron, string, iron, red, green.
2. Nothing will be shown in the output, even though it's a valid recipe!
3. If you move the green bulb to a different empty slot, then the output will show.
4. If you proceed to move items around, you might bump into both of these issues, it'll get stuck on the wrong bulb pattern or it won't show output.

Workaround:
This bug does not occur if you set Universal Tweaks config B:"Crafting Cache"=false