I was playing Equivalent Skies modpack for a while until this strange thing appeared in my base. I can't destroy it and I don't know what it is. It just destroyed a part of my ME system. I hope someone knows more about this and which mod it is from.
The Flux Rift is an immobile entity added by Thaumcraft 6. It spawns when Flux in the local chunk's aura exceeds 75% of the chunk's Vis cap. Flux Rifts are a source of Void Seeds, Primordial Pearls, and Taint.
Be sure to move away from it, because
Every 30 seconds, the rift will drain some Flux from the aura to slightly increase in size. If the rift would extend into a block, it will break that block, unless it is unbreakable. Fully stable rifts cannot drain Flux to grow.