Broadly speaking, violence has been up in Europe post-lockdowns. Something about having a lot of people with few ties to a community, having no economic prospects and strained welfare systems. Then add the EU's self-destructive path in order to "stick it to Putin".
For Sweden in the particular, I believe they also have an idiot compassion problem in their judicial system beyond even most "progressive" justice systems. So for example, if you're under 15 you cannot go to juvenile jail in Sweden because it does not exist. End result, gangs were recruiting 15s and under. I'm not entirely sure if Sweden ever got around to changing that.
For Sweden in the particular, I believe they also have an idiot compassion problem in their judicial system beyond even most "progressive" justice systems. So for example, if you're under 15 you cannot go to juvenile jail in Sweden because it does not exist. End result, gangs were recruiting 15s and under. I'm not entirely sure if Sweden ever got around to changing that.