This isn't so much a Thaumic Augmentation issue, but it's worth signal boosting - due to a critical log4j library vulnerability, everyone on 1.12.2 should update to at least Forge version 2858 immediately. At the very least, do not join any multiplayer server until you are sure you are on version 2856 or later (2858 is the latest as of when I am writing this).

The following is only applicable to developers running the mod in a development environment - if you are a normal player, the following does not apply to you!

This is the info I've been waiting for. Hadn't had time to look into what has developed. I'll be updating my server shortly. Curiously MultiMC said they already fixed it before I heard news of the exploit. So all that should be necessary is to update my modpack so it points to the latest Forge then?

The dependency chain is a bit confusing when mods get involved, but pretty much MultiMC is able to override libraries, so they pushed a fix of their own. This only will fix it on clients, of course, and I'd suggest updating anyway, if only for everyone not using MultiMC.