Evening @tradertall, sorry for the delay in getting back to your thread here. (looks like @harrrrrry has provided the link to find Private Discussion so hope that has helped you now located any you may have)
For any thread that is removed, we do reach out to the original poster to let them know. This is usually only needed if there is a duplicate thread, or a post that goes against the Community Guidelines. They may also not have been soft deleted but possibly merged to another thread.
It's also worth noting, that members are able to soft delete their own posts (within 10 minutes of creating it), so what you could also be seeing is members soft deleting their own posts.
If there is something specific though that you are referring to, please do let me know and I can look into it 🙂.