This is due to a peculiarity of RLV. In earlier times of RLV you'd have to include the attachment point in the name of the attachment, or put it in a folder containing the name of the attachment point so that RLV would know where to attach it.
While in current RLVa implementations this isn't needed anymore (it will restore the attachment to its default or last-worn position), this functionality is still active.
So if you put an attachment into a subfolder named "top", it will get attached to the "Top HUD" attachment point. The same goes for any other attachment point names, such as "bottom", etc. So, if your top is in a subfolder "top" and it is rigged mesh, you will see it correctly, despite it being attached on a HUD attachment point. To others, it will be invisible, though.
To fix it
- rename your folder; it must not contain "top" or "bottom"
- manually attach your problematic attachment to a non-HUD attachment point. You have to do this only once to reset the attachment point.