it's a known bug.
you'll have to regen the aura nodes following this :
"Yes, you heard that right. You can add all the ores, trees and other worldgen features to existing worlds by changing a few things in your config files. Remember: this could be risky so always backup your saves beforehand.
- If this is the first time loading Thaumcraft with that save, you can leave the regen_key setting as 'DEFAULT' otherwise set it to anything else.
- You need to choose what to regenerate. I strongly recommend you set aura_nodes to 'true' if this is the first time you are doing this. Without the aura you won't be able to do 99.9% of the things you could in Thaumcraft.
- Run the game. It will lag for a while and you should see some console spam about chunks being regenerated. This is fine - just wait it out. It shouldn't take too long. If the world had been explored a lot you might see the message reappear every now and again. This is also normal.
- If, for some reason, you wish to do this again or somehow your savefile got corrupted and your aura nodes have gone missing, all you need to do is set the regen_key value to something else. Any word would do.
IMPORTANT: If you chose to generate TC ores and such in an existing world It is best to keep the config as-is. Do not switch everything off again after running the game or server once. As you explore chunks that have been explored in the past, but you haven't visited yet the new TC will regen in them as well. If you turn it off before you get a chance to revisit them nothing will be genererated and you will have to do the regeneration from scratch to add it to those chunks which could cause doubling of ores and nodes."
btw there is another thread on this issue so you can use the search bar next time
