We all know that wearing a full set of void thaumaturge armor in thaumcraft will double the defense of the armor. But when I installed the latest version of TA, its double defense effect disappeared. I am sure this is caused by TA, and sincerely hope that you can fix it.
English is not my mother language, sorry for the inconvenience.

This isn't a bug. The "double armor" display is actually a Thaumcraft issue - I'm not sure whether it was intended to show the extra damage reduction caused by the armor or just a bug, but the end result is it makes people very confused. I kept getting asked why that was a thing (especially with the void boots not doing that), so I removed it. There is no gameplay change made at all, the armor is unchanged in how much it protects.

If it really bothers you, you can add thecodex6824.thaumicaugmentation.core.transformer.TransformerVoidRobesArmorBarFix to disabledTransformers in the config, but I don't think I will be reverting this.