It's most likely because you are participating in a Subreddit that has a CQS or comment karma requirement. Often times what happens is if you don't meet that requirement, your post/comment gets removed. Whether it's an aged or new account, all it takes is just ONE removed comment/post from an automoderator for your account to be toast.
What you need to do is slowly warm your accounts up, whether aged or new. That means for the first day, focus only on browsing and upvoting random posts manually. You may throw in 1-3 comments. But make sure you ONLY comment (do not post) on Subreddits that have absolutely no CQS or karma requirement. This way your comment sticks. As you gradually grow your karma (doesn't need to be a lot), you can throw in more comments a day. I think you need to do this for a few days then your account is effectively warm. Also, make sure you do not delete any comments/posts because it may affect your CQS.