Hi there -- I took a look at your last three mailings and found that most of those soft bounces were labeled with a pretty general server reply code: 450 unknown path. This usually means that the recipient's inbox is full or that the server has reached a temporary limit for incoming messages. Since it's a soft bounce, those addresses will remain in active status so that you can send to them again!
If you're seeing a spike in soft bounces, you might want to adjust the time you send your mailings. That might make a difference!