Versions

Betweenlands version:

3.4.9

Forge version:

14.23.5.2838

Singleplayer or Multiplayer:

Both.
Vanilla Server.

Installed mods:

Baubles 1.5.2
Just Enough Items 4.15.0.287
Thaumcraft 6.1.BETA26
ThaumicJEI 1.6.0-27
The Betweenlands 3.4.9

Description of the problem

How to reproduce:

If not familiar with Thaumcraft:

1. Do "/tc research Player all", then "/xp 100"

2. Get a Focal Manipulator, a Workbench Charger, a Blank Greater Focus, a Caster's Gauntlet, and one of the the following Vis Crystals each: Potentia, Alkimia, Vitium

3. Place the Workbench Charger on top of the Focal Manipulator, right click to open GUI.

4. Put in the Blank Greater Focus amd select Bolt, Scatter, Cloud, Flux in this order and hit the green Anvil Button the make the Focus. Don't close the GUI while it's doing its thing.

5. Take the Focus out and press F while holding the Gauntlet to select the Flux Cloud Focus (click the Focus in the radial menu)

6. Go to the Betweenlands and search a fortress. Get to the boss. When the sphere shows up, hit it with a Flux Cloud by right clicking the Gauntlet.

Expected result:

I expect the Boss to take damage in the Flux Cloud.

Actual result:

The Boss simply vanishes, the music stops and the fight is over. No drops or anything.

Hm okay that's bizarre. I'll try to reproduce it.
Meanwhile, please report this to Thaumcraft too. Thaumcraft's source code isn't publicly visible so I can't look at it to try and find the cause.