Vertices disappeared on some objects (not all). I'm trying to merge 2 vertices at center, but nothing happens when I select 2 vertices, and select that option. I'm very new to Blender editing. I've searched YouTube, and all Stack Exchanges, only old references come up, nothing about this issue. Please help.
In my image, you can see, there are no vertices on the 2 right objects. Even for the left two, I cannot merge any of those vertices together. All 4 objects will eventually be merged, but I can't merge if there are no vertices to do so with.