It is one thing for bitcointalk to add criteria for building your profile. It is quite another for your posts to disappear over time. Are the admins deleting some of my posts? If so, why? I am not spamming and I'm not posting frivolous comments.
Here are some possible reasons:
1) The thread were you made reply was deleted. It happens in case you are posting reply to a thread on repetitive topic.
2) Only Your posts were deleted. Sometimes you will get notification for this. This can be because of making irrelevant or off topic posts.
Solution is to avoid posting on useless threads especially they are quite new.