Check the messages carefully. They may look like duplicates, but it is probably the case that there are comments being posted to the thread. Since subscription messages all begin with the original post, they look the same at the top. Scroll down to read the new comments. If that is not the case, then it is possible that the original posts are being updated, in which case you are likely getting the updated versions. If you don't want to get updates, you can turn them off in your subscription settings. If neither of these explanations holds and you are getting multiple copies of every piece of subscription content then something else is wrong. Try turning off all your subscriptions, logging out, logging back in, and turning on your subscriptions again.