A Dark Souls 2 "softban" is essentially an exile into a realm of cheaters: Softbanned players can continue to play, but their online interactions are limited to other softbanned people—a much smaller pool of players than would normally be available. It's typically a punishment meted out for cheating, but Kotaku reports that a growing number of Dark Souls 2: Scholar of the First Sin players are saying they've been softbanned simply for using the DS2fix mod.
DS2Fix, as the title suggests, clears a number of technical issues with Scholars of the First Sin, including a significant weapon durability bug and a couple of big crash bugs. It also, according to its Nexus Mods description, will not trigger softbans. And mod creator Alessanro De Micheli told Kotaku that, unless the game itself has changed, he's confident DS2fix isn't the problem.
"Unless Fromsoft patches the game to recognize DS2Fix64, it cannot be detected (because the game doesn’t know what to look for)," he said. "So, the only logical conclusion here is that the game is actually flagging any hook / injector—that means that even by using x360ce, SweetFX, ReShade, DXTory or the Durazno Dead-zone fix for controllers will put users at risk of getting banned. Being DS2Fix64 the only ‘SotFS-made’ tool available it also is the most exposed one to accusations—players would likely think DS2Fix is at fault, not anything else they’ve been using for years."
A lively argument about whether or not DS2Fix is the culprit is underway in this Reddit thread, among others, which unfortunately just highlights the fact that nobody really knows what's causing the softbans. It's quite possible that DS2Fix is the problem, despite De Micheli's insistence that it's not, and in fact the sheer number of complaints has prompted him to reach out to Bandai Namco for official confirmation, one way or the other.
We've done the same, and will update if and when we receive a response. In the meantime, we strongly recommend avoiding the DS2Fix mod, and other injectors like SweetFX with Dark Souls 2, until the situation is cleared up. Better safe than softbanned, right?