Soft blockers are things that get in the way of developing software more effectively or efficiently. Development is not prevented, as woud be the case with a 'hard blocker', it is merely slowed down.
By analogy, consider both a beaver dam and a human-made dam. For water to flow around the human-made dam, the dam would have to be destroyed (at least partially). It is a complete blockage of flow. A massive effort is the only effort that can be made to get past it. On the other hand, a beaver dam can be flowed around. It is an incomplete, or soft, blockage of flow. No effort has to be made to get past it. Water can just flow around it. This makes the effort required to remove the dam seem all the more wasted. Instead, spend no effort and just live with the inconvenience of low flow. Flow around the negligible obstruction. But, over time, the dam can grow and grow until the flow has slowed considerably. Meanwhile, from one day to the next, no one notices the change.
The insidious nature of soft blockers is what makes them so dangerous. The effort required to remove a soft blocker is greater than the effort required to work around it. So, you work around it. This slows the flow of development.
Particularly malignant soft blockers will grow slowly, without being noticed, until it has substantially inhibited the progress that would have otherwise been made.
Hard blockers get addressed often, and effort is generated to remove them. Soft blockers don't get addressed often, and potentially no effort is generated to remove them.
In unhealthy organizations you can be penalized for "wasting time" trying to remove soft blockers. In healthy organizations, their removal might never be prioritized.
In conclusion, fear soft blockers. Avoid them. How? I don't know.